Here's the basic gist of the site: Up to five people can act as their own DJs and play any music that they want to play in a given room. And the site's music selection is REALLY good, just about anything you can think of is on there, even the music of today. Those in the room (including DJs) decide if the song being played is "Awesome" or "Lame".
Here is the ATRL room for turntable.fm!
Three catches:
1) In order to access turntable.fm, you must be friends with someone on Facebook who is already on turntable.fm.
2) You can only play three songs from one album and four songs from one artist every three hours (I think this is how it goes).
3) It has been brought to my attention that only United States citizens can take part. Sorry, my foreign brethren.
Anyone that wants to sign up and join in on the fun should talk to me or JGib, particularly if you need someone to add as a friend to get on the site. Trust me, it's worth it.
EDIT: If you are interested and are not in the Facebook ATRL group, now would be a REALLY good time to join. It would make adding you to turntable.fm easier, if need be.