Really long article in today's NYTimes re: the fall of Friendster, the first mainstream social network. Gary Rivlin does a relatively good job summarizing all the things which can doom a hot Internet property - bad tech architecture, out of touch VCs, poor strategic decisions by founder. However he leaves out the "fakester" controversy, when Friendster started policing its community and removing fake profiles like "Jesus" or "Cookie Monster."
While these profiles only represented a small percentage of the site they were really important as ways of expression - you make Cookie Monster your friend and this would be another way of projecting your interests and personality. And removing them with zero tolerance also smacked the community in its face w/ a clear "Friendster isn't yours, it's mine" attitude. Besides its technical stability I believe MySpace benefited from the fact it was just that - your space - a template you could use rather than a form you needed to fill in.
[note: I met with Jonathan Abrams about Friendster in 2003 when I was transitioning out of Linden Lab and right before I joined Google. We didn't really click so it was just a brief conversation.]
* Brady from O'Reilly also suggests that the Fakester fallout was an important part of Friendster's demise