I used to date only nerd guys who had little experience with girls. It was (well, is) a big turn-on for me to break em' in. But I have found that these guys are not the greatest boyfriends so I've had to stop dating them.
With women, I am insanely attracted to smart, cute, curvy girls... with few exceptions. If they don't know how cute they are, even better.
I guess I like both my men and women a little bit more innocent than I. ;)