Chatroulette, and the Secret Behind the Web's Most Addictive Site

I've been trying to figure out why Chatroulette.com -- the randomized video-chat website that's been getting a ton of press lately -- is so compulsively addictive, and I think I've got it. I've been thinking about this because I spent close to two hours on that damned site last night, two hours that I could've spent sleeping, working, cleaning my apartment or catching up with my actual, non-virtual friends.