How Does Grooveshark Compare in Quality to Others?

I enjoy listening to Grooveshark online http://listen.grooveshark.com/ and I like what I hear on my Boston Acoustic BA735 computer speakers. I love the wide variety of free music available in all genres, especially some obscure and great classic jazz (sometimes complete albums!) Almost every kind of music and artist you may want to hear is there. The quality of many of the music tracks is pretty good too. I've listened to Pandora's free music, and LastFM, but I don't care for restrictions on the number of tracks you can listen to, skip etc. Grooveshark provides freedom, flexibility, and allows you to customize your listening to the way you want it. What do you think of Grooveshark and how does it compare to others like it?