I don't do anal, as others have said before me... the single greatest organ in the history of organs is mere millimeters away, why stick it there instead?
Now, personally, I never got the whole 'things in the ass = gay' part either. There are gay men who don't even do anal, ask around. But no matter what keep in mind that just because her genitals aren't being pleased, doesn't mean she isn't (in fact, considering prostate placement, you have more reason to want to be fucked in the ass than she should). Sex is a lot more than that, and giving her the chance to be the 'penetrative one' gives a lot of new angles to approach the artform.
I know that if there was a woman I was close enough with, I find the whole idea of her 'turning the tables' and fucking me for a change to be really hot. I have yet to do his though as I don't know how best to approach a woman about it... any pointers out there?