Share 'Nice Guys'

Why do women claim to want nice guys? I've read it in books, seen it in music and experienced in real life. I mean, I'm a relativly nice guy- ask me to stay up for 12 hours to do a project with you and I'll obliege. So, women generally claim to want a nice guy, and that the last ex was a "real bastard". So, why is it that us "nice guys" fall into the friends catagory, rather than the "I wish I ...