I rather like the Twanalysis website!
Basically, they scan your twitter account and make a few sweeping judgements based on your tweeting habits etc.
The results based on my account can be accessed below:
I especially liked:
Tips for your tweeting…
Your tweeting is already tip-top! No improvements needed – but check back here every so often to make sure your reputation is being maintained!
So if that fills you with intrigue, feel free to follow me on twitter; http://twitter.com/DarkAeon