It's synchtube, and the way it works, is you and friends can add links to this playlist. Once you're all satisfied with it, the admin lets it play! My friend and I have added a few videos in the playlist, and while it's kinda fun with just the two of us, we'd like to see just how fun it'd be if we had, like, n more people.

http://www.synchtube.com/r/xtii

Thats quite a cool idea, having a look at what videos you've all added, but really, who would have time to watch it all?

Heres a "cool" site I recently found: http://chaosinyourtown.com/ (I find these sites that use Google Streetview data pretty cool, theres a couple of others I don't remember)