The main difference between Spotify and GrooveShark is that GrooveShark has always been a webapps while Spotify is a desktop application.
But htings have changed since from now on you can use GrooveShark right from your desktop without even having to open the web browser thanks to GrooveShark application.
Now, thanks to a fan called Ruy, we can enjoy free music from GrooveShark using a desktop application. It's very useful if you think now you can minimize it and control music as you are using any other media player.
The program offers all you can find in the website: track search, playlist creation, genre, author and album clasification and a curious 'radio station' that will play songs similar to the one you are listening to.
Without any doubt, Grooveshar application is a good application for those Grooveshark users out there.