15 of us were female, girlfriends or wives of male members.
every guild I've ever been in, there's always been a fair few chicks
There's also "I'm a girl and I play wow" group on Facebook with 1600 members in, and it's a quiet group
As for playing female toons, who knows. I know alot of chicks that hide behind male toons and don't speak to avoid unwanted attention
My guess would be between 20-30% of playerbase as female