Zopa is an amazing little experiment in lending and borrowing money (UK only right now):
Here’s the really clever bit. An individual lender doesn't lend to an individual borrower because that’s too risky. Instead a lender lends their money across at least fifty Zopa borrowers, and similarly a borrower borrows from a group of Zopa lenders. So the risk is well and truly spread.
I saw it via sippey and liked Ben Hammersley's comments on it.