I just caught wind of an amusing application via False45th called the Last.fm Mainstream-O-Meter. If you have a Last.fm account you can just pop in your username and it will compare your listening habits to anyone else who has listened to that artist, and then spit out your “mainstreamness.” You can check out my results here, anyone got me beat?
Sidenote, I think I’d prefer they named it “mainstreaminess,” taking a page out of Colbert’s book.