The RIAA isn't going after people who download. They're going after people who UPLOAD. If you have more than 1000 songs in your upload library, you get on their lawsuit list.
The RIAA simply logs into the P2P service, tracks your IP number, and serves a subpoena on the ISP to get your address.
Don't fall for the poor innocent victim single Mom in this. The daughter is a hard core music uploader with at least 1000 songs in her upload library.
I think my original point was lost somewhere along the line. The story implies that the industry has some way of tracking who downloads. I say they don't.