Groovylists makes Grooveshark playlists from iTunes, Last.fm, or Spotify
Groovylists can't import playlists bigger than 200 songs, so you can't use it to pull in your entire library at once. It also can't make songs that aren't on Grooveshark magically appear there. If the 'Shark doesn't have the songs you need, you'll have to upload them yourself.
The sudden popularity of Groovylists means it occasionally hits Grooveshark's API rate limit and stops working for a while. There's not too much Groovylists can do about the problem, other than setting up a partnership with Grooveshark to get the rate limit lifted (we can hope!), so just be patient and try again later if it's not working for you.
UPDATE: We've received word from Groovylists that there was a fix for the rate limit problem, and everything should be working as normal again!