Clearinghouse ChillingEffects logged 12,000 DMCA cease and desist notices, some for a single URL and others like for The Pirate Bay containing hundreds.  Across all categories and territories, the music industry led the list. Details:

The international music industry, represented by the trade group IFPI, issued the most DMCA take down notices in 2010: 1272 in total.Most IFPI notices contained dozens of offenders each.  The RIAA followed some film and media organizations to come in 7th place with 203 DMCA take downs.

Sony/Epic/Estate of Michael Jackson claimed the 11th spot, followed by indie Stones Throw Records at 12th and Chappell & Co at 13th according to TorrentFreak.