Update: You no longer have to be invited by someone to get in.
The good news: There's finally an app for Turntable.fm.
The bad news? You're probably not going to get to use it. Turntable.fm still requires you to be invited via Facebook by someone who is already using the service. This is probably a good thing from a scale point of view, but I think Turntable.fm may have worse things to worry about when it does open the floodgates.
Turntable.fm is a mix between streaming music service, chat room and ultimately, videogame. If you try to be a DJ, you'll enter a room and essentially compete against other DJs to have your playlist selections played in the room. You can, of course, simply listen and vote as a lowly listener, but for people looking to waste hours of time at work the real challenge is producing a great playlist and not getting booted. There are "gamified" perks within the service as well, like new avatars to unlock using a points system.
Turntable.fm has been quite popular with the tech set, and as announced at TechCrunch Disrupt today, it's raised $7 million in its latest round of funding. Apparently Turntable.fm turned down some offers in a gambit to get Fred Wilson of Union Ventures to sit on its board (which he will do). What's rather interesting is that several celebrities have invested in this latest round, possibly hinting that Turntable's popularity could be spurred by some high-profile users. But we'll see if investors like Jimmy Fallon show up to strut their stuff.
The iOS app is a faithful recreation of the website, shrunk down into portable size. CNET has a great how-to on getting started and does a good job of explaining the ins and outs of Turntable.fm overall. About the only thing you can't do in the app is monkey with your profile and avatar. Check out the app on iTunes here.