emacs-fu

I have just released mu/mu4e version 0.9.9. There are quite a few changes, both user-visible and 'under-the-hood'. I've also spent some time on improving the manual (pdf), and I'm quite happy about it.

Some of the more visible new things in mu4e are:

• Support for crypto (decrypting messages, signing them)
• Support for refiling (like mutt, Wanderlust)
• Dynamic folders (instead of hard-coding the sent/draft/trash/refile folder, they can be functions that return different folders based on the message we're dealing with, see the example below)
• Same for the folder to save attachments
• A lot of smaller and bigger UI improvements

Also, the core mu program has seen a lot of improvements (many of which directly improve mu4e as well)

• Better support for non-ascii locales / character sets, such as ISO-2022-JP
• Improved on-line help ('mu help ...')
• Performance improvements for threaded display (~ 25% for 23K messages)

For a more complete list, see NEWS.

As mentioned, mu4e now supports dynamic folders. Before, you'd set your trash folder to some static string:

(setq mu4e-trash-folder "/trash")

In some cases, you may want to have a bit more flexibility – for example, have a separate trash-folder (or sent-folder, drafts-folder, refile-folder) for private mail and work mail. You can now do something like:

(setq mu4e-trash-folder
 (lambda (msg)
 (if (and msg ;; msg may be nil
 (mu4e-message-contact-field-matches msg :to "me@work.com"))
 "/trash-work"
 "/trash")))

After I have dealt with some e-mail, I either delete it or move it to some archive folder – refiling. For this, there is now the r keybinding, and mu4e-refile-folder; and a place where dynamic folders really shine:

(setq mu4e-refile-folder
 (lambda (msg)
 (cond
 ;; messages to the mu mailing list go to the /mu folder
 ((mu4e-message-contact-field-matches msg :to
 "mu-discuss@googlegroups.com")
 "/mu")
 ;; messages sent directly to me go to /archive
 ;; also `mu4e-user-mail-address-regexp' can be used
 ((mu4e-message-contact-field-matches msg :to "me@example.com")
 "/private")
 ;; messages with football or soccer in the subject go to /football
 ((string-match "football\\|soccer" (or (mu4e-message-field msg :subject) ""))
 "/football")
 ;; everything else goes to /archive
 ;; important to have a catch-all at the end!
 (t "/archive"))))

How cool is that? After reading my inbox folder, I select all messages (C-x h), press r, and they're all moved to the right refiling folder.

mu4e already supported signing/encrypting messages, but now it supports decryption and verifying signatures as well. This was one of the most requested new features. I think it is still a bit rough, but it has been working very well for me.

I think version 0.9.9 is a great new step for mu4e. It already goes far beyond I ever planned to do. I received a lot of suggestions for new features, which is great! I'm not planning to implement all of those, but I will try to make mu4e even more programmable – it should be easy to augment mu4e with your own little elisp-snippets – the Barbapapa principle of software, already so clearly present in emacs itself.

So, how can we set this up? First, install BitlBee – many distributions have ready-made packages, otherwise you can build from source. In the examples below, I am assuming you are using Bitlbee version 3 or higher; if you use a different version, the details will vary a bit.

You can either run Bitlbee as a system-wide daemon, or just use it on your own. I am doing the former (for the latter, bitlbee.el is useful).

To connect ERC to the Bitlbee daemon, you can use something like the following:

(defun i-wanna-be-social ()
 "Connect to IM networks using bitlbee."
 (interactive)
 (erc :server "localhost" :port 6667 :nick "user"))

I'm sure you can come up with a better nick than user… Anyhow, with this function in your ~/.emacs, we can connect to bitlbee with:

M-x i-wanna-be-social RET

This should connect us to BitlBee; when all goes well, this will look something like this:

*** You have joined channel &bitlbee
*** mindcrime has changed mode for &bitlbee to +t
*** Users on &bitlbee: @user @root
*** Topic for &bitlbee: Welcome to the control channel. Type help for help
 information.
<root> Welcome to the BitlBee gateway!
<root>
<root> If you've never used BitlBee before, please do read the help
 information using the help command. Lots of FAQs are answered there.
<root> If you already have an account on this server, just use the identify
 command to identify yourself.
<root> The nick is (probably) not registered
*** &bitlbee modes: +t
<ERC>

Now, this first time, you will need to register yourself (this is only needed once); use the same nick (user in the example) that you used before:

<user> register user secretpassword
<root> Account successfully created

We're registered! This means, that bitlbee knows about you, and will save your settings.

Just to complete the bitlbee-connecting part: the next time you want to use bitlbee, use i-wanna-be-social as before. However, now you need to identify yourself (rather than register):

<user> identify user secretpassword
<root> Password accepted, settings and accounts loaded

This can be automated by adding something like the following to your config:

(defun bitlbee-identify ()
 (when (and (string= "localhost" erc-session-server)
 (string= "&bitlbee" (buffer-name)))
 (erc-message "PRIVMSG" (format "%s identify user secretpassword"
 (erc-default-target)
 djcb-bitlbee-password))))
(add-hook 'erc-join-hook 'bitlbee-identify)

Modify user and secretpassword as desired. If you don't want write out your passwords in your emacs config files, take a look at keeping your secrets secret.

Now, let's add some IM-accounts (just some examples here; also see Bitlbee Quickstart. Note, add any point during this, you can see your accounts with the command:

<user> account list

and using the numbers (or the accounts 'tag') you can switch an account on (and off):

<user> account 0 on

There are many other commands – use help command the consult the built-in documentation.

To connect to IM networks, you have to add the accounts to BitlBee. It will save them, so you only need to do that once. Let's do it - in each case, replace user and password with whatever you use for those.

You can see your combined logged-in buddy list using M-x erc-channel-names (or C-c C-n). Or use the blist command (see help blist).

After adding an account, it's a good idea to issue the save command, to ensure that bitlbee saves it.

Jabber

<user> account add jabber foobar@jabber.org mypassword
<root> Account successfully added with tag jabber
<user> account jabber on
<root> jabber - Logging in: Connecting
<root> jabber - Logging in: Connected to server, logging in
<root> jabber - Logging in: Converting stream to TLS
<root> jabber - Logging in: Connected to server, logging in
<root> jabber - Logging in: Authentication finished
<root> jabber - Logging in: Authenticated, requesting buddy list
<root> jabber - Logging in: Logged in

GoogleTalk

<user> account add jabber myaccount@gmail.com foobar
<root> Account successfully added with tag gtalk
<user> account gtalk set oauth on
<root> oauth = `on'
<user> account gtalk set nick_source full_name
<root> nick_source = `full_name'
<user> account gtalk on
<root> gtalk - Logging in: Starting OAuth authentication

<jabber_oauth> Open this URL in your browser to authenticate:
https://accounts.google.com/o/oauth2/auth?scope=https://www.googleapis.\
com/auth/googletalk&response_type=code&redirect_uri=urn:ietf:wg:oauth:2.0:oob&client_i\
d=78312399893489.apps.googleusercontent.com
<jabber_oauth> Respond to this message with the returned authorization
token.

<user> 4/sIns904fdlkP5nudjCF4mBHF7Go_-E0g8
*** jabber_oauth is AWAY: Offline

Facebook

<user> account add jabber myusername0@chat.facebook.com
<root> Account successfully added with tag fb
<root> You can now use the /OPER command to enter the password
<root> Alternatively, enable OAuth if the account supports it: account
 fb set oauth on
<user> account fb set oauth on
<root> oauth = `on'
<user> account gtalk set nick_source full_name
<root> nick_source = `full_name'
<user> account fb on
<root> fb - Logging in: Starting OAuth authentication

<root> fb - Logging in: Requesting OAuth access token
<root> fb - Logging in: Connecting
<root> fb - Logging in: Connected to server, logging in
<root> fb - Logging in: Converting stream to TLS
<root> fb - Logging in: Connected to server, logging in
<root> fb - Logging in: Authentication finished
<root> fb - Logging in: Server claims your JID is
 `-748234518@chat.facebook.com' instead of
 `myusername0@chat.facebook.com'. This mismatch may cause problems with
 groupchats and possibly other things.
<root> fb - Logging in: Authenticated, requesting buddy list
<root> fb - Logging in: Logged in

<user> account fb off
<root> fb - Signing off..
<user> account fb set username -748234518@chat.facebook.com
<root> username = `-748234518@chat.facebook.com'
<user> account fb on

MSN / Live Messenger

<user> account add msn partygirl89@hotmail.com iamcute
<root> Account successfully added
<user> account msn on
<root> msn - Logging in: Connecting
<root> msn - Logging in: Connected to server, waiting for reply
<root> msn - Logging in: Transferring to other server
<root> msn - Logging in: Connected to server, waiting for reply
<root> msn - Logging in: Authenticated, getting buddy list
<root> msn - Login error: Error reported by MSN server: Invalid
 (non-existent) handle [12:17]
<root> msn - Logging in: Logged in

Other accounts

Now, chatting is easy, following the normal ERC conventions (and settings). When people talk to you, a window opens (or a frame – see erc-auto-query. And you can initiate conversations with people by using /msg nick, with nick of course being the nickname of the person you want to talk to.

ERC/Bitlbee also work together nicely with Sauron, the emacs event tracker.

Have fun! I have only scratched the surface here - you now have the full arsenal of Elisp and ERC power available for your chatting.

So - what to do? First, you can set the input-method, as explained in the emacs manual. This is the best solution if you're writing a non-Latin language – Russian, Thai, Japanese, …

If you only occasionally need some accented character, input methods like latin-postfix (e" -> ë), latin-prefix ("e -> ë) or TeX (\"e -> ë) are useful. They also tend to annoy me a bit, as they often assume I need an accented character, when all I want is to put a word in quotation marks…

Another method is to use a special compose key; for example, under Gnome 3 it's in the the Region and Language applet, under Options..., in Gnome 2 it's in the Keyboard applet in Layouts/Options…. This works for all programs, not just emacs (see this Ubuntu help page for some details). I've set my Compose-key to Right-Alt, so Right-Alt "e -> ë.

Using the compose key works pretty well for me; setting the input method may be more convenient when you need to write a lot of accented characters.

Now, his may be good and well for the accented characters and other variants of Latin characters, such as the German Ess-Zet ligature "ß" (note, you can get that character with latin-prefix "s -> ß, latin-postfix s" -> ß or <compose-key> ss -> ß). But what about Greek characters? Mathematical symbols? Smileys?

One way to add characters like α, ∞ or ☺ is to use ucs-insert, by default bound to C-x 8 RET. If you know the official Unicode name for a character, you can find it there; note that there's auto-completion and you can use * wild-cards. For the mentioned characters, that would be GREEK SMALL LETTER ALPHA, INFINITY and WHITE SMILING FACE.

You can also use the Unicode code points; so C-x 8 RET 03b1 RET will insert α as well, since its code point is U+03B1. In case you don't know the code points of Unicode characters, a tool like the Character Map (gucharmap) in Gnome may be useful.

Since ucs-insert may not be convenient in all cases, you may want to add shortcuts for oft-used special characters to you abbrev table. See the entry on Abbrevs in the emacs manual. I usually edit the entries by hand with M-x edit-abbrevs, and I have entries like:

(text-mode-abbrev-table)
"Delta0" 0 "Δ"
"^2" 0 "²"
"^3" 0 "³"
"almost0" 0 "≈"
"alpha0" 0 "α"
"any0" 0 "∀"
"beta0" 0 "β"
"c0" 0 "©"
"deg0" 0 "℃"
"delta0" 0 "δ"
"elm0" 0 "∈"
"epsilon0" 0 "ε"
"eta0" 0 "η"
"heart0" 0 "♥"
"inf0" 0 "∞"
"int0" 0 "∫"
"notis0" 0 "≠"

Now, alpha0 will be auto-replaced with α. I'm using the 0 suffix for most entries so I can easily remember them, without making it hard to use alpha as a normal word. Note, abbrevs are a bit picky when it comes to the characters in the shortcut – for example, setting != -> ≠ won't work.

If you have set up a nice set of abbreviations for text-mode, you may want to use them in other modes as well; you can accomplish this by including the text-mode abbreviations into the table for the current one, for example in your ERC setup:

;; inherit abbrevs from text-mode
(abbrev-table-put erc-mode-abbrev-table :parents (list text-mode-abbrev-table))

In the past, I often used straight LaTeX for such things; I wrote my thesis with it, but also many other documents. There are many things I like about LaTeX, one of them being that I can use emacs for writing. Still, there are also a few things I do not particularly like. First, I think LaTeX is quite heavy with formatting directives, which hinder my writing flow (e.g., when I want to include an image, a table or a source code snippet). Another thing is that I find the default LaTeX styles a bit boring. Nothing wrong with it, but there just too many documents with the exact same lay-out.

Now, back to org-mode. One way to use org-mode is as a friendly way to generate LaTeX (and, consequently, PDFs). This is a big improvement! Much more than LaTeX itself, org-mode allows to focus on the contents of the document, rather than instructing LaTeX what to do. This comes at the price of small bit of flexibility, but, if needed org-mode allows you include straight LaTeX when needed – so while keeping easy things easy, hard things are still possible. The latter does require a bit of experience with LaTeX a though.

Now, for the second issue, the way documents look, there are other solutions, and they live on the LaTeX side of things. I'm sure many have seen The Beauty of LaTeX. Using the XeTeX implementation of LaTeX and the fontspec package, you can create LaTeX documents with a bit 'refreshed' look.

So, the steps to get this working with org-mode:

• install the texlive-xetex packages on Ubuntu and Debian (this installs a huge set of packages)
• install the SIL fonts (I'm using ttf-sil-gentium and ttf-sil-charis, but there are more)
• I'm also using DejaVu Mono (ttf-dejavu)

We now need to define some LaTeX document class for org-mode that uses XeTeX and some of these new fonts. Let's call the document class djcb-org-article (as I often use the djcb- prefix for my own stuff), it could be something like the following (add to your org-setup – e.g., in your .emacs, make sure there is a (require 'org) before this:

;; 'djcb-org-article' for export org documents to the LaTex 'article', using
;; XeTeX and some fancy fonts; requires XeTeX (see org-latex-to-pdf-process)
(add-to-list 'org-export-latex-classes
 '("djcb-org-article"
"\\documentclass[11pt,a4paper]{article}
\\usepackage[T1]{fontenc}
\\usepackage{fontspec}
\\usepackage{graphicx} 
\\defaultfontfeatures{Mapping=tex-text}
\\setromanfont{Gentium}
\\setromanfont [BoldFont={Gentium Basic Bold},
 ItalicFont={Gentium Basic Italic}]{Gentium Basic}
\\setsansfont{Charis SIL}
\\setmonofont[Scale=0.8]{DejaVu Sans Mono}
\\usepackage{geometry}
\\geometry{a4paper, textwidth=6.5in, textheight=10in,
 marginparsep=7pt, marginparwidth=.6in}
\\pagestyle{empty}
\\title{}
 [NO-DEFAULT-PACKAGES]
 [NO-PACKAGES]"
 ("\\section{%s}" . "\\section*{%s}")
 ("\\subsection{%s}" . "\\subsection*{%s}")
 ("\\subsubsection{%s}" . "\\subsubsection*{%s}")
 ("\\paragraph{%s}" . "\\paragraph*{%s}")
 ("\\subparagraph{%s}" . "\\subparagraph*{%s}")))

Of course, this can be customized to your own preference; e.g., North-Americans may not be using A4-paper.

org-mode takes care of the export from its own format to LaTeX, but we need to tell it to use xelatex to process the LaTeX to PDF:

(setq org-latex-to-pdf-process 
 '("xelatex -interaction nonstopmode %f"
 "xelatex -interaction nonstopmode %f")) ;; for multiple passes

That's all that's needed on the setup-side.

Now, let's create a little test document, test.org, to show how it works:

#+LaTeX_CLASS: djcb-org-article
#+TITLE: My little document
* Introduction
 
 This is my document. There are many like it, but this is mine. It's easy to
 write without *too* _many_ /distractions/.
 
** Normal distribution
 Probability density of the normal distribution, using familiar TeX notation
 for formulae:
 
 $$\frac{1}{\sqrt{2\pi\sigma^2}}e^{ -\frac{(x-\mu)^2}{2\sigma^2} }$$
** Some table
| *Greek God* | *Roman God* | *Element* |
|-------------+-------------+----------------|
| Zeus | Jupiter | Sky and clouds |
| Hera | Juno | Family |
| Poseidon | Neptune | Sea |
| Hades | Pluto | Underworld |

We can export this to a PDF using C-c C-e p (or C-c C-e d to automatically open the PDF in a PDF-viewer). This should all work nicely; if it doesn't, note that when exporting, say, test.org, org-mode will create a file called test.tex, and visit in a buffer. There's also a buffer with the output from various commands, but sometimes it can be useful to run LaTeX (xelatex in this case) on the file by hand, to find any problems. The wonderful org-documentation about exporting to LaTeX has more information.

I think the result is pretty nice – it stays true to the class LaTeX article class, but freshens it up a bit with some news font. If you can make something better – which is not unlikely – you are of course invited to contribute your own!

org-mode is a pretty convenient way to write nice-looking PDFs. Combined with xelatex, they don't have to look too plain :). However, I'm aware of my limitations when it comes to the coolness/aesthetic aspects, but I hope others can show the way here.

Maybe org-mode could ship with a number of ready-made templates to make it easy to make nice-looking documents, resumes, reference cards, reports, meeting notes and so on.

When dealing with e-mail, one particularly important feature for me is the ability to search my messages. In fact, it's so important for me that I wrote some software to do this for me; the software is called mu; it indexes the messages in my Maildirs, and then allows for searching them using queries, based on message contents, headers, or other message properties.

mu works through a command-line interface, although there is an experimental GUI available as well. The command-line interface makes it possible to hook mu up with various mail-clients, such as mutt, or Wanderlust. Some Linux distributions ship mu, but since the versions they ship are often a bit outdated, I recommend building it yourself from the sources linked on the mu website. The process is fairly straightforward; and there is plenty of documentation in the form of man pages.

I've been combining mu and wanderlust for a while (see mu and wanderlust - the old way, below), but this week Sam B. on the mu mailing list showed a way to do so in a much more elegant way - using virtual or query folders.

How does this work? Well, after installing mu, add the following to your Wanderlust setup file (~/.wl or it's moral equivalent – see the older Wanderlust posts for the details):

(require 'elmo-search)
(elmo-search-register-engine
 'mu 'local-file
 :prog "/usr/local/bin/mu" ;; or wherever you've installed it
 :args '("find" pattern "--fields" "l") :charset 'utf-8)
(setq elmo-search-default-engine 'mu)
;; for when you type "g" in folder or summary.
(setq wl-default-spec "[")

So, to start with the last part, whenever you type g in folder or summary, in the mode-line you will get something like Folder name (.inbox): [. Now simply type your mu search expression and press Enter, and wanderlust opens a (temporary) folder with the search results. Brilliant!

Next, to add virtual folders for searches you do often, simply add some folder specifications like the following to your .folders file (again, check the older Wanderlust posts if you're not familiar with folders-file):

VFolders {
# message I received today
 [date:today..now]!mu "Today"
# messages bigger than 1Mb 
 [size:1m..100m]!mu "Big"
# signed messages i got in 2010 related to emacs
 [date:2010..2011 flag:signed emacs]!mu "Signed-Emacs2010"
# unread messages
 [not flag:seen]!mu "Unread"
# or (for mu >= 0.9.4):
# [flag:unread]! mu "Unread"
}

After this, restart Wanderlust, and there you go! Wanderlust will display your brand new virtual folders with an icon that looks like a little whale.

You can put arbitrary mu search expressions between the [], matching whatever is useful in a certain case. Check the mu documentation to see how to do this.

Note, the messages you get in these virtual folders are links to the original messages. In practice, this means that changes you make to the links do no affect the originals – if you delete a link you're not deleting the message.

This discussion would not complete without a description of the old way I used search. This method may still be useful for integrating mu with other clients such as mutt.

What I've been using for a while is a (in retrospect) rather clumsy way to integrate message searches with Wanderlust: based on the results of a query, I would create some special Maildir and fill it with symbolic links to the matched messages, and the visit this special Maildir with Wanderlust. I'll include the code here to contrast it with the more elegant solution that we saw before, but also because the approach taken might be easily adapted for other mail-clients.

;; search using mutt
(defvar mu-wl-mu-program "/usr/local/bin/mu")
(defvar mu-wl-search-folder "search")
(defun mu-wl-search ()
 "search for messages with `mu', and jump to the results"
 (let* ((muexpr (read-string "Find messages matching: "))
 (sfldr (concat elmo-maildir-folder-path "/"
 mu-wl-search-folder))
 (cmdline (concat mu-wl-mu-program " find "
 "--clearlinks --format=links --linksdir='" sfldr "' "
 muexpr)) 
 (rv (shell-command cmdline)))
 (cond
 ((= rv 0) (message "Query succeeded"))
 ((= rv 2) (message "No matches found"))
 (t (message "Error running query")))
 (= rv 0)))
(defun mu-wl-search-and-goto ()
 "search and jump to the folder with the results"
 (interactive)
 (when (mu-wl-search)
 (wl-summary-goto-folder-subr
 (concat "." mu-wl-search-folder)
 'force-update nil nil t)
 (wl-summary-sort-by-date)))
;; search by pressing 'Q'
(define-key wl-summary-mode-map (kbd "Q") ;; => query
 '(lambda()(interactive)(mu-wl-search-and-goto))) 
(define-key wl-folder-mode-map (kbd "Q") ;; => query
 '(lambda()(interactive)(mu-wl-search-and-goto))) 

After installing mu and putting the above in your wanderlust startup file, you should be able to search by pressing Q. The mu documentation has an example for mutt as well.

It's straightforward to integrate advanced searching capabilities to Wanderlust using mu, and thanks to Sam B., it's gotten a lot easier! The second (old) approach may be useful as 'inspiration' for use in other e-mail clients as well, if they do not provide the kind of hooks that the first solution needs.

Let's first look at how it all began: source code blocks. I guess most org-mode-users will be familiar with those: the ability to include syntax-highlighted ('font-locked') snippets of source code in org-documents. We discussed source blocks before, they look like this:

#+begin_src perl
sub my_func {
 print "Hello, world!\n";
}
#+end_src

And note that code blocks can be edited in their 'native mode' using C-c'= (or, =org-edit-src-code).

When code block like this are exported to, say, HTML, they'll look like the following fully highlighted snippet (assuming you're reading Emacs-fu in it's full-color version):

sub my_func {
 print "Hello, world!\n";
}

org-babel takes this a few steps further: instead of just looking at source code, we can actually evaluate (execute) it, using the org-mode-based system called org-babel.

If you have a recent version of org-mode (7.x or later), add the following to your .emacs (or equivalent):

(org-babel-do-load-languages
 'org-babel-load-languages
 '( (perl . t) 
 (ruby . t)
 (sh . t)
 (python . t)
 (emacs-lisp . t) 
 ))

This enables org-babel for the mentioned languages; there are many other languages available as well.

Now, suppose we have a snippet of python in an org-mode-buffer:

#+begin_src python
def hello(str):
 return "Hello, " + str + "!"
return hello ("dude")
#+end_src

You can move the cursor (point) inside the src-block and press C-c C-c (or, org-confirm-babel-evaluate). This causes the block of code to be evaluated (executed), after asking you for confirmation. The result will inserted below the block, like:

#+results:
: Hello, dude!

Note, in the hello example, the result of the block is the value of the evaluation - that is, the value of the last expression evaluated. This is the also the default, so we don't need to (but could) write:

#+begin_src python :results value

The alternative is to use the (standard) output of the function, which is activated with :results output, e.g.:

#+begin_src sh :results output
 echo "Hello $USER! Today is `date`"
#+end_src

Moving to this block and pressing C-c C=c would get you something like the following – probably with a different username and time:

˜#+results:
: Hello djcb! Today is Sun Feb 27 13:51:50 EET 2011

org-babel also allows you to refer to the code blocks from elsewhere in your document, by labeling your code-blocks with srcname. Let's say we have some Ruby code to revert a string:

#+begin_src ruby
def revert(s)
 if s == "" then 
 return ""
 else
 return s[-1].chr + revert(s.slice(0, s.length()-1))
 end
end
revert(str)
#+end_src

We can now 'call' this block; note that we get the result of evaluating the block. So if you want to use the result of a function in the block, you also need to add the call to that function (see the last line).

Now, we can use:

#+call: revert(str="VeryCoolStuff")

And we get:

: ffutSlooCyreV

Note, due to some limitation/bug in my version of org-babel, the strings should not contain spaces or other special characters, so the following will give result in an error note:

˜#+call: revert(str="Very Cool Stuff")

Whenever you try to evaluate a code block, emacs will ask for confirmation -- this is important, because of the obvious security implications of executing unknown code. Anyway, if you do trust the code, you can use the following to skip the confirmation:

(setq org-confirm-babel-evaluate nil)

These simple examples do not really capture the power that org-babel brings, but it's a start. There is quite a bit of documentation for org-babel to help you further. Finally, if you are already using org-babel, feel free to share your experiences in the comments!

You can store any kind of secret data in your encrypted files. One type I find particularly useful is to store account data (user names, passwords) for various services there. For example, I use the emacs identi.ca-mode client, which gets its account data through variables identica-username and identica-password.

I do not want to put this information in my main .emacs file for safety reasons, but instead, put it an encrypted file, together with the account data for other services (mail, twitter etc.). Emacs' require does not understand encrypted files, but load-library does. To deal with that, I have two files, secrets.el and secrets.el.gpg (in my load-path):

;; secrets.el
(load-library "secrets.el.gpg")
(provide 'secrets)

and

;; secrets.el.gpg
(setq identica-username "djcb"
 identica-password "$ekr3t")
;; ... other passwords ...

Now, in my .emacs I have a function for various services, like:

(defun start-identica ()
 (interactive)
 (require 'secrets)
 (identica-friends-timeline))

This will prompt me for the password, but only if I use anything that requires the secret data, and only once per session.

Update: as Richard notes in the comments, you can also use require by explicitly specifying the filename (parameter two). That might actually be easier -- thanks Richard!

By default, EasyPG performs symmetric encryption; if you want to use public key encryption instead (useful when you want to share the encrypted files with others), you can use:

;; 'silent to use symmetric encryption
;; nil to ask for users unless specified
;; t to always ask for a user
(setq epa-file-select-keys t) 

The 'users' in this snippet are the people in your GnuPG-keyring – EasyPG lists your keyring inhabitants, allowing for easy selection. You can also specify the people who can decrypt your file by putting something like the following at the beginning of the file you want to encrypt.

# -*- epa-file-encrypt-to: ("foo@bar.org") -*-

EasyPG brings more functionality for encryption, decryption, signing, managing your keyring and so on, but I haven't used that much yet. Anyhow, the automatic support for reading/writing file is really nice.