Peerflix has launched a P2P DVD trading service after a year of beta testing. The P2P network is a pay-for network, and is legal (apparently). The essential idea is that you list the DVDs you own in their database, and people can request the DVDs... which you then send. It isn't digital transfer, but it's the same concept of sharing - Pass it along as you use it. Although this idea doesn't seem that novel at first, that is almost exactly what NetFlix is, aside from NetFlix having a central collection of DVDs.
According to some, this is a legal grey-area, due to what is called "first-sale" doctrine. According to their attorneys, however, it's acceptable - Because Peerflix is charging for the service of organizing the lists. Interesting.