Valve has taken the next logical step for Team Fortress 2's bustling hat-based economy, by introducing actual money into the equation. The Steam "Community Market" entered beta today, a test bed that allows users to exchange Steam Wallet funds for items instead of simply trading.
The beta only works with TF2, and even then only with consumable items, but Valve promises it will be available with other titles next year. You can show off your items on the Community and sell or trade them to other Steam users. According to a FAQ, all sales are final. Steam keeps a 15% transaction fee during the beta period, which may increase in the future. During the beta, sales are restricted to 200 per calendar year, starting with January 1. Presumably you won't reach 200 before then.
"With over a half million trades made every week, the trading system has been very successful," said Valve's Tony Paloma. "Extending game economies beyond trades and giving players a way to turn gameplay into funds for new items and games is a key component for moving that success forward."
So to summarize: Team Fortress 2 started with clothing items, which led to barter and trade, and finally the advent of currency. Use this handy metaphor to teach your kids about the development of economics in western civilization, because it happened exactly the same way. That progression is almost definitely because of this guy.