Craig Newmark, founder of craigslist, gave a speech about his site and why he thinks it works as a virtual community. I have very little experience with his site, which he describes as a collection of classified ads, but forums have allowed an interesting community to form around them. Since the ads are organized by city, the site has become a user supported collection of city guides.
I found his talk personal, humorous, and engaging. You can access his Powerpoint slides here. Craig’s an affable fellow who’s dedicated to his work, and as of late, various social/political causes.