The economy of paperbackswap.com
I just joined paperbackswap.com. You post books you own that you're willing to send out and can have other people send you their books. I wanted to do it to get some use out of some old books we've had sitting around the house.
The economy of the web page is interesting. When you join and post 10 books, you are given two credits. For every book swap, the requester is charged 1 credit and the sender receives 1 credit. So, the economy activity of the web site generates no wealth; all transactions are even. The only way wealth is created is when a new person joins. I never took even one economics course, but that sounds like trouble to me.
The obvious first fear is hoarders. It would be simple for lots of the credits to pile up with people who aren't requesting books, maybe because they just don't use the site anymore. That drains the money supply. A tight money supply makes people less willing to spend money (here, request books). So, you'd see very little swapping.
I'm planning to check out the forums and see if people are discussing the economy and if there are any signs that the tight monetary policy is having a negative effect.
By the way, I posted 16 pretty random books and I've already had 6 requests. So, my anecdotal evidence is that the economy hasn't stagnated. My current fear is that there is some reason to make a bunch of requests of newcomers.