These are cumbersome in that you have to get online, get an address of the next person to send it to, package up the dvd, and send it. The shipping costs are also non-negligable when we're shooting for $1 per rental or less.

A better idea would be to have bulk trades. If people have movie collections of 100+ movies, surely I'd be intrested in 20 movies out of most people's collections, and surely somebody would be intrested in a big swath of my movies. I could indicate movies I want to see and it could match me up with someone who has many of those movies, then I could also grab several more out of their collection to make for a total of 20 or so movies. When the requesit collatoral (like 'peerbux' in the case of 'peerflix.com') changes hands, the other guy goes to the post office and ships me my movies in bulk. Now I have a few months worth of movies after just one transaction.