There are many types of yeast in the world. Sacharomyces is just one type of yeast. And most sacharomyces species do not make good beer. There's no reason to think that all yeasts would be good for making beer.
The vaginal yeast is called Called candida. Have you ever smelled a yeast infection? There is a very, very, very good reason why no one would ever make Candida beer. I guarantee you, no one would want to make a beer that smells literally like shit or like week-old fish.
It's been done, at least once : http://www.thestranger.com/seattle/Content?oid=23562
If you plated your girlfriends vag and really isolated a single yeast colony (sans the other funky bunch), and grew up a starter, and brewed a beer with it - would you drink it? Would your friends drink it, if you told them where the strain came from?
I personally wouldn't have a problem tasting it, if it was isolated in this manner. Just another wild yeast. I doubt it would taste like beer, though.
I think that the vast majority of people think that they would get some other microbiota in there. There's a huge difference between isolating a wild yeast and having some skank dip their meat curtains in your beer.