I always assume people on the internet are male unless I'm on twitter or facebook or something with an avatar or I know the user. I don't really assume too much and tend to focus on the story or point without their gender coming into play. Even though I'm female and it mildly annoys me when people make this assumption, I have yet to figure out a way to break this habit. I agree it is a bit disorienting when you come to the realization that their gender is something you didn't expect.

I remember reading something on some forum years ago that was a girl talking about her boyfriend. About halfway through they mentioned something about gay stereotypes and I remember thinking that was odd and irrelevant. Couple sentences later it FINALLY penetrates my thick skull that it was a gay guy talking about his relationship. I felt idiotic and had to reexamine everything I had read and assumed with this new information. I remember not that much changed. Turns out relationships have their ups and downs and struggles and amazing moments whether it's between the same or opposite sexes.

I used to get upset when people would say "Thank you sir" or refer to me as a "he" but it doesn't really bother me anymore. On reddit, if I'm trying to make a point or say something in a bigger subreddit, I kind of like it if it is assumed I'm male because I feel like my real point comes across more and the "OP is a female" distortion glass doesn't come into play. This might mostly be my imagination.