It's a little bit different than Grooveshark and Pandora. You don't choose the music, the music comes to you. But it really has a nice navigation system, if you don't like the song they're playing, you can use your arrow key to go onto the next song.
Also! A really cool thing about The61 is you have these quests you can do to earn hearts and reputation points. You can support artists by "hearting" their music and reputation points to bid on songs you like and "revive" them. I've always been a fan of games with quests, so it was easy to get into. The quest themselves are real easy and simple: listen to the hottest songs, listen to songs in the "mood" section, listen to the61 late at night, and so on.
Anyway, if you sign up, you're referrer was unfrightful! I'm totally sure if I get referring points or something, but it must do something since the it asks you when you sign up.