interesting thoughts. i found this facebook app (http://apps.new.facebook.com/lendinglibrary/?pa...) that kinda does what you're talking about. i think it does a good job with the business logic part of things, but some kind of localization (i.e. restricting to your network or geographical area) would be helpful.
it would take a critical mass of people who are willing to make things available for this to work ;)