I took these videos at Sessions... Castpost has had some server issues over the last week, but I'm happy to link to them here anyway.
We've got the Intro, Bruce Spector talking about how some of the big names in the web space got started as social endeavors, Dick Costolo talking about user contributions, Yochai Benkler, Umair from Bubble Generation, Jeff Jarvis and Tim O'Reilly.