I knew that people trade all sorts of stuff besides stocks. Fantasy Sports is a form of trading...you make educated guesses based on how well you think the players are going to do. And if you think the player's not going to do well in the future, you try to trade it for someone else that another player is willing to part with.
People also trade weather! So it seemed brilliant to me when I saw Blogshares, a place where you do can fantasy trading on blogs.
It seems like any complex system on the edge of chaos are systems that people like to trade. Because if something was completely predictable, it would be trivial. Everyone would know which the best pieces were, and wouldn't want to trade once they had it. If it was a system that was completely random, I argue that people wouldn't trade either, because the only heuristic that would work with minimal effort is to choose and trade randomly. I'm not sure why, but it's my experience that people don't like that, especially if something's at stake.