i use Grooveshark too. Good for finding specific tracks rather than radio listening. Not sure what "meta" info you get about the music (I suspect none, or very little). Also good if you are away from you own personal music collection as you can save/retrieve your own playlists in GS.
also, there are greasemonkey scripts for it. only tried one - removes the ads on the right and automatically replaces them with lyrics of the song that's playing. very handy when you want to singalong to the latest Justin Beiber hit (whoever he is).