Fakester
Another link from Boingboing before I go: an SF Weekly (where in this case SF means San Francisco) article titled Attack of the Smartasses, detailing the adventures of the "fakesters" who sign up for Friendster under various aliases, fake names, and fictional identities.
I think the idea's kind of fun (I was tickled when I came across "James" (Kirk) on Friendster, especially when there was a testimonial to him by "Khan"), but I have to admit that the attitude described in the article—a sort of "Hey, this place was lame, but then we came along and made it interesting, the company should be happy we're here" kind of thing—doesn't hold much water for me. It's a free service provided by a for-profit company with a particular set of rules; much as I like art that happens in the interstices of such services (like the funny fake reviews on Amazon), I have a hard time sympathizing with people who talk as though they have a right to break the services' rules.
But I do think it's an interesting point that everyone on such a service is fake in some sense.