bsdewhurst sends along an interesting article about how MediaSentry and the RIAA identify file sharers. Since 2003, while the RIAA has been filing 28,000 lawsuits, the percentage of US Internet users using P2P for downloading music has dropped from 20% to 19% (there is no knowing how much of a factor the lawsuits have been). The list the RIAA uses for ISP takedown notices is about 700 currently popular songs that are updated based on the charts, so not liking the top 40 could save you. The list of songs tracked for the user-litigation program is said to be larger.