Got nothing against it honestly as long as it is for the right reasons (well right for me).
I'll play games with opposite sex leads no problem, as well as characters in fighters and fps games that have opposite character, like in Time Splitters.
I don't even have a problem with people playing custom opposite sex character, if it's for the sake of playing from a different perspective (ie, different scenes and phrases for the character, like in Mass Effect).
However I personally don't like to play as a custom female character (I'm male btw) because of the following reasons:
I don't play video games to oggle the opposite sex (which most of the people I know who play the opposite sex do it for this reason).
I find it harder to find my self in the rol of a female (like in games like Mass Effect and Oblivion). I just like my version of this character but be well, like me. I make the choices I would make if it where me in the game. So yeah it kinda messes with my immersion factor.
So in short I'll play a female if she is the lead, but if given the choice I'll stick my own gender thank you
