Ed Felten from the Freedom to Tinker blog has written a post with Princeton senior Sauhard Sahi called Census of Files Available via BitTorrent. The survey takes a random sample of files available on a trackerless BitTorrent system. The article is full of caveats--discussion happening in the comments--but does dig into the likely copyright status of the works they found.

From Boing Boing

They have evolved

Great and somewhat pertinent cartoon.