According to a post on JP's blog, JP received a message from Twitter with a URL to the tweet that was being removed, noting that the reason was because of a DMCA takedown notice. The tweet in question was a link to a blog post on his site posted on April 20. The post described a leaked album by The National, a link to the Amazon page where the album could be preordered, and two links to MP3s from the album, both of which were hosted elsewhere (Box.net and Mediafire).
via arstechnica.com