I'm not a woman, but...

How aware are you of the gender or sexual orientation of other LW participants?

As for gender, I start with an about 90% prior probability (from the last survey results) that they are male, and update it according to what I read (most often the username alone is enough to bring the posterior to epsilon or 100% minus epsilon). As for orientation,I don't really care: I know EY is straight but he'd like to self-modify to become bi, and I think Alicorn is bi and lukeprog is straight but I'm not fully sure. That's it. I have read by comments by others mentioning their orientations but I can't even remember them.

Do you mentally assign a gender to each LW user whose comments you read, or who replies to you?

As in aliefs? Usually but not always. (And sometimes the alief is wrong. For example, there's a LWer who, despite having an obviously feminine username, comes across to my alief system as male (not sure why) and there's a Wikipedian (with an apparently feminine username, but he has explained that it's actually a Latin neuter plural and he's male) who comes across to my alief system as a female -- likely because of his username and because of the dingbats such as smileys, heartsuits and musical notes he uses to express his mood. I even called him 'she' by accident a couple times.)

Do you react differently based on the gender of other commenters?

I try not to. And in discussions which don't have anything to do with gender I think I almost always succeed.