I've assumed that the RIAA was monitoring BitTorrent downloader/uploaders. Now I've come across this report (not sure how credible it is) of such monitoring: Bit Torrent downloading:

So here I am, downloading through various torrent apps, various music torrents, all probably illegal. My first day, so I've learned the ropes, a little, and already blocked Sony North America, The Australian Broadcasting Corporation, RIAA and some others, I didn't recognise late last night. They were scanning my torrents, looking down my ports, or trying to.

Of course, I'm still sort of wondering why we haven't seen many DMCA notice-and-takedowns for BitTorrent seeding sites yet.