Using it for my favorite character in the book I'm writing. I figured that I could use the Americanized pronunciation to make a more accurate impression on readers. It also helps me convey the eccentric naming patterns of my world, and of Siv's hometown.
Minor, but this is the name of the mother (a spotted owl) of the eponymous Hoole in the children's book series Guardians of Ga'hoole. It was the first time I'd heard the name myself, I had no idea it was connected to Norse Mythology.
Siv Widerberg, a Swedish poet bears this name. Some of her poems were my favourites as a child, therefore I'll always have a positive feeling about this name.
Simple yet comely, would be a great middle name as opposed to the overused Lee or Marie. It can work out as a first name too, with a more developed middle name. Anyways, I like it.
When I first read the Myths of the Norse, I came across this name, but spelled "Syf", and even though it may not be correct, I must say I still prefer it that way. It seems a little prettier and more feminine, more Goddess-like. :)
My mother is called Siv and she always says nobody names their daughters this. But maybe it will come again. I don't know anyone under 40 years who bears the name Siv.