InterTwitter has a simple idea that works well if we were in a dating service on Twitter. Ok, I am joking. It is a good way to match compatibility between users and seeing how many friends and followers they have in common.
THE DRAWBACK: Due to Twitter limiting what is returned to them (per their site), you only get counts. Not exact usernames! When you run the tool is breaks down percents and gives the following output:
Share 38 following / Share 198 followers
Until they get the actual usernames and build around it, this is just a statisitical tool.