Anonymous – That sounds similar to Cringely’s somewhat complicated Snapster system. It would be fun to set up a P2P system that send an AAC file to someone else, authorize them, let them play the song, and deauthorize them. Perhaps even renting out your collection for $0.01/play, meaning you could quickly turn a profit on your purchased music collection.
In that scenario, your profit/loss would be linked to the number of purchased songs in circulation and the demand for songs. A sort of speculation market would spring up where people would buy songs that few other people bought but they expected to be popular.
Unfortunately Apple would put the kibosh on it pretty quickly through technical and legal means.