On the Internet, no one knows you're a frumpy, uncharismtic shy person.
I nearly always create some sort of fake identity for online use, and after reading all of Turkle's accounts of people who are so heavily invested in their online lives and multiple identities (to the point of outright obsession), I wonder if part of it is that I can imagine myself getting "sucked in". If a website requires that I register before I can view the page's content, I submit ridiculous information, partly as a disguise, and partly in hopes that someone, somewhere will get the message that I don't appreciate attempts to collect information about me. I have never used an avatar, and I admit I've always found them to be sort of silly, but I've realized that in situations like this very blog, avatars would help me remember who's who.
Like some others have mentioned, I was also sort of shocked at the amount of real money that moves around as a result of Second Life. I can't really relate to the desire to pay for a cartoon on a screen, but I guess if shopping for cartoon land and clothes helps people exorcise their consumeristic urges without having to actually go out and buy a bunch of stuff, I'm all for it. In Aspects of the Self, Turkle quotes a college student who admits there is a part of him that is like the violent characters he creates, and an online identity is a relatively harmless space to act out. (p.190) I'm sure we could all agree that however upsetting a personal attack in an online environment may be, it's infinitely better than having to experience/witness such antisocial behaviors in real life. And it's not as if social consequenses don't exist online-- I spent some time looking at the police blotter in the Community section of the Second Life board, and it seemed like the most common crimes were the use of weapons in the wrong space, sexual harrassment, and spamming. The listed transgressors were punished by being denied access to the site for a period of a few days, and presumably would be welcome to return if they mended their ways.