There's a new social network for gamers called GamerLibrary. The site takes the Delicious Library and Shelfari angle by letting users compile, and show off, their gaming collections, while at the same time adding a request feature to let members trade and borrow games among themselves. The idea is that you'll be able to join with your small collection of games and get others to loan you theirs, assuming they see something they like in your library. Together you build up a larger pool of shared games that can be borrowed or bought on the side.
Of course where this utopian idea falls apart is the trade mechanism. On one hand, GamerLibrary is taking the stance of aiming its service at groups of friends so swaps and trades can be made in person. On the other hand, if it's expecting people to use this service with strangers, in situations where a swap requires shipping, forget about it. I think people are far too lazy, or cautious, to use a service like this extensively unless there's a built-in ease of use, which is why DVD and game-by-mail services like Netflix, Blockbuster, and Gamefly have become so popular using prepaid and addressed envelopes.
If GamerLibrary really wants to get an edge on some of these subscription-based mail-order services, it could create a hybrid service, charging a small fee to the renter, while offering users who are sharing their own library a discount or credits toward future rentals depending on the size of their library. GamerLibrary could then sort out who wants want and send out prepaid, anonymously addressed envelopes that would go through a central processor. Although, this system could lead to many unpleasantries, including lost or damaged game discs, and little or no incentive for high-volume renters over a subscription service.
If you're looking for a way to organize swaps amongst your buddies, this is a handy solution--assuming you're willing to put in the time to add all your titles. I could also see this being a killer Facebook app, as you're more likely to make swaps and advertise what you've got using an existing social network than joining a new one.