The Interactive Advertising Bureau (IAB) produced a solid "status report" of the various sites and platforms currently powering social media and user generated content.
Though the report was released in April, 2008, it's still a good read for management, advertising and marketing executives to get a good understanding of the various platforms out there on the WWW.
Here is the UGC Platform page and the full report can be accessed here: User Generated Content - Social Media and Advertising
Happy content generating!!!
