The $30 is actually dirt cheap. It's a music streaming app with a library of about 22 million songs. The $30 is for an annual membership.
By comparison that's 3 months (or 2 for multiple devices) worth of Rhapsody which has 10 million songs. Although I have used Rhapsody and there are pros and cons to each. Rhapsody has more organized search results, but Grooveshark allows you to search other users playlists, which is where I am finding a lot of new great music.
Overall the amount of music you can find and the overall interface on Grooveshark is better. But I'm learning now that it's quite buggy in this latest 2.08 revision. I'm hoping for a quick move to 2.09 and hoping they add scrobbling to last.fm like their desktop/laptop version does.
Overall though it's awesome to have so much music on demand at all times.