The RIAA and MPAA would probably have to sue half of the people in the US, since probably that many people are using Bittorrent (like me), but I don't download movies, just anime fansubs, and then I buy the series when it gets licensed. I support the industry so that they can make more series in Japan, and the American licensors (ADV, Geneon, FUNimation, ect) can license more series.

ADV will send out letters to people who happen to be hosting links to downloads of ADV's series as well as the fansub groups that are fansubbing ADV series that are located in the US or wherever ADV happens to have a license requesting to take down the downloads as well as the links. Guess what... people listen, and they do what they are told.