I've been using it for a while now, and just want to pass it on to those that don't know about it.
No commercials, you can make stations based off artists and then it plays songs similar to the artist as well. It's really good at doing so, and if you don't like a particular song, it wont ever play it again and it adjusts to your liking. Pretty awesome!
You can use it without signing up, but it will eventually ask you to sign up, which is FREE and takes 1 minute. I recommend you sign up so you can save settings and that such.
LOVE THIS THING! I find artists I wouldn't normally know about!