UPDATE: 20 JUNE 2010

Due to significant changes in the Twitter API Authentication (oAuth implementation) this application requires repair. I will attempt to resolve this as time allows. - DBI

In hopes to learn more about what could be accomplished via the Twitter API, I wrote an application called CommonTweeps recently. Inspired by the Mutual Friends feature presented on Facebook I decided Twitter could use the same functionality.  When someone follows me I often wonder how they found me.  Using CommonTweeps I'm able to determine this information (provided they aren't following me via an automated channel).   Further, if we have mutual friends or followers I am more likely to follow them back.  Give it a go by visiting http://commontweeps.com