I've been using it for a few weeks now. I absolutely loved the concept, it basically takes two old music websites - Songza and Jelli Radio - and mixes them together to make streaming songs (usually in a select genre) chosen by and voted on by users. (When I first joined, however, I was expecting that the DJs would literally be remixing the songs live haha; maybe someday live remixes will be an option, could be interesting!)
At first I thought the points system was great - it made people choose the best songs for each room because they wanted to gain the most points from the listeners. This meant that you were always listening to great songs for each room. I quickly found out, however, that it had severe drawbacks. DJs are so desperate for points and/or they don't *actually* know much about the genres (they're just there for the points) that they tend to play the same top songs over and over (they seem to find lists of top x-genre songs on websites like Last.fm and exclusively play those songs). A lot of the DJs might not even actually be present, they use a bot to grab a DJ spot and then make a long list of songs while they're AFK.
The developers have talked about their future goals for turntable.fm and it seems really interesting. Among their ideas was the ability for artists to DJ and you could listen in, it would be just like an online concert. Say Deadmau5 were to DJ, you might even be able to pay and DJ right beside him. Now, personally, I would find that much more cool if the songs were actually being played live somehow, otherwise I could have just listened on Grooveshark/Youtube without all of the lag. I'd like to see Last.fm scrobbling in the future, an ability to see who's in the room (it's impossible to find certain users in crowded rooms), a better voting system (in rooms with lots of people, most are AFK, so your vote doesn't have much value if no one else is voting), and if possible move away from Flash (I believe they're planning to move to HTML5).
And so, although the concept is awesome, I was burnt out quite fast; also, turntable.fm has been crippled more and more in order to remain legal, making it increasingly less fun. I think I'll stick to Pandora for now, maybe I'll drop by turntable.fm in the future if a friend wants to listen to some songs with me.
Turntable.fm is in invite-only beta; in order to get in you need a Facebook friend that's already in or you need to receive an invite via email. If you need an invite, go on turntable's fan page (http://www.facebook.com/turntable.fm
). There's always people on there offering the ability to add them as a friend on facebook in order to log on turntable.fm (after getting in, feel free to un-friend the person).