Being online makes you think a lot about identity. You meet somebody in some kind of interaction -- a usenet newsgroup back in the day (and still), Slashdot, chat, an online forum -- and you are usually very conscious that it is your persona interacting with their persona. After a while you realize that this is true even if you are not trying to create multiple personas ... people perceive you through their expectations, and they're expecting a persona, so that's what they'll see.
Personas are severely underrated by most people -- they can be a lot of fun and interesting and you can sometimes build up enough trust to get to "the next level" and closer to the "real" person (whatever that means). Baudrillard to the contrary, there are differences between "persona" and "real"; but there is certainly a continuum rather than any absolutes. (Another false duality?) But there are also many different ways of measuring personas, and there is kind of even a language for talking about this, things like As real as she says she is. There are protocols (ceremonies, technically) for exchanging information at many different levels, tracking identities as they change over time and learning from their evolution (including whether it is generally trending "more" or "less" "real").
The online community in Pattern Recognition is a good reproduction/representation of some that I've been in. Dennis Cooper describes another, much more twisted one. Much earlier there was a wonderful online seduction in Microserfs that rang very true. Each gets its own texture. Many people try to make it as positive a texture as they can -- either by instinct, from experience, from analogies toother communities ... many people don't realize this, in which case you try to teach them; or don't care, in which case you try to change their mind. Control is an illusion; influence, however, is possible, and you might as well make it as seductive as you can.
Things and people crossover from online to the "real world" and/or in the other direction. Weird connections happen -- sometimes genuinely by coincidence, sometimes from bizarre miscommunications, sometimes from software bugs.