Very interesting. We've touched on the reasons for gender bending in game a few times before, and there are all kinds of reasons why people play as characters of the opposite sex, from staring at an attractive behind to garnering more money and attention (or less attention) from other players, to roleplaying a character.
But really, none of that matters too much-- it's just a game, and for whatever reason, people are welcome to play it as they please. A better question might be how you refer to the gender of other players. I've gotten in trouble a few times here by referring to players on the forums (including CMs, way back when I started) as one gender when it turns out they're actually another, so eventually I just decided to call it how I see it: if someone plays a female character I call them "her," and a male character gets called "him." For people playing a different gender, sure, it might come off a little strange. But it comes with the territory, I guess, of pretending to be someone else for a while.