Google, Facebook and the MPAA take sides in a copyright case over the DMCA safe harbor

Big dogs like Google, Facebook, the Electronic Frontier Foundation, and now the Motion Picture Association of America have all filed briefs in an obscure copyright case currently being heard by the 7th Circuit Court of Appeals. At stake: what does a service have to do when a takedown notice is filed, and should that site have an additional burden to block repeat offenders?