In the NY Times Magazine Paul Krugman provides an overview of the intellectual battels in economics over the last 50 years (link).
In the article Krugman cites a famous example published of a baby sitting co-op. The idea was that each parent would get 20 coupons When someone watched their kid they gave that person a coupon for each 1/2 hour of babysitting. As the story goes unfortunatly people wanted to have on hand more than 20 coupons so people where unwilling to use the coupons for fear of not having enough. This was used as an example to show that more coupons should be printed so people would spend them and babysitting would happen again. Which is an analogy for what federal reserve can do, when people aren't spending $s, print more of them.
I was thinking of this while checking out the website Goozex. The website works that you can trade video games and movies. Send someone a movie and you get points, want to get a movie then you cash in your points. The key to the system is that you can buy more points, so it isn't closed. Goozex sets the points price of each game . Unlike the babysitting co-op the price can be changed if Goozex sees a surplus or shortage of say Rock Band or Forrest Gump.