Thanks to a kind fellow from Last.fm a new web app of mine called ScrobbleShark appears to be working. If you are one of the 100 people on earth who uses both Grooveshark and Last.fm - and one of the 10 who also want your Grooveshark plays scrobbled to Last.fm - then check it out. It supports automatic and manual scrobbling so you can try it out at first, just be sure to click 'pause scrobbling' after setting it up because automatic is the default option.
It's really easy to use. You login with your Google account, authenticate with Last.fm, enter your Grooveshark username, and you are up and running. I need some beta testers so if you only use Grooveshark, why not join Last.fm and give it a shot?
There are apps to visualize your listening history and other fun stuff. You can also meet people who have similar tastes in music, if you want to. It's really cool! Grooveshark is a great player and Last.fm is great for the community and data mining possibilities. ScrobbleShark helps you enjoy the best of both services.
Let me know what you think if you try it.