TorrentFreak has a few interesting items: Video: How People Are Tracked Using BitTorrent and Director of ‘The Nines’ Talks to TorrentFreak About Piracy. Making the Movie had more thoughts in Torrent Ambivalence.
Mark Pesce's talk about harnessing mob rule downloading last year is still interesting. Back to the point, here's the simple version of how people are tracked using Bittorrent:
Update: An interesting discussion broke out in the comments of the FreshDV post, John August on BitTorrent and Piracy.