See Rheingold's Brainstorms for Virtual Worlds Resources (especially the Critiques section). Howard Rheingold has a lot more to say about this subject; check out his book, the The Virtual Community.

I've been thinking a lot about virtual community -- are they even possible? I'm finding that I'm a lot more comfortable talking online with people once I've met them in person. Surely this isn't the way it was supposed to work? People have been tackling these issues for years, but there's no sense of history on the internet; there's no debris, no cruft and accumulation, no way to tell that groups have made these journeys before. How to build "community"? And what is it?