The "Reading Race Online" made an interesting point about racial stereotyping online. Although it would seem that there should be little racial stereotyping when we can't see the people we're interacting with, Burkhalter suggests that there may actually be more racial stereotyping for that same reason! It's easy to assume that another person online must be of the race stereotypically associated with their views or behavior. Even if they claim otherwise there's no need to take their word for it, since people can lie about such things over the Internet.
This is an interesting idea, but I'm not sure if things often happen that way online. I suspect that white Internet users tend to just assume that everyone else online is white too, unless they explicitly say otherwise. I don't think I've ever seen anyone's claims about their own race challenged in an online community.
Maybe I'm wrong, though. I do know that in online communities people sometimes make incorrect assumptions about what sex other users are, and this does tend to be associated with gender stereotypes. Someone who seems coolly logical must be a man, someone who seems overly emotional must be a woman, etc.