Valve has announced a new exchange system that allows gamers to trade their Team Fortress 2 equipment for Steam games. Currently in beta, Steam Trading will partially resolve a fundamental flaw with any barter system: sometimes you can't obtain what you want because you don't have a tradable item that interests the other party. TF2 players have attempted to avoid this issue by using various forms of scrap metal, which is required by most in-game crafting recipes, as a form of currency.
When that isn't suitable, players sometimes trade Steam games (solely on the honor system), and it's not unheard of for people to exchange real money over external services like PayPal. Unfortunately, those situations expose both parties to the potential of being scammed. Although Steam Trading won't allow the direct transfer of real-world currency, users can purchase a giftable title desired by the item holder. Most people have a lengthy wishlist, so it shouldn't be too difficult to settle on exchange terms.
Again, only tradable games apply, such as duplicates in your library or those that you've specifically purchased as a gift. Your single copy of Borderlands with 50 hours logged isn't eligible. When you receive a game through trading, you can redeem it on your account or trade it again. Valve will make it easier for you to acquire tradable games. The company has added a new checkout option that lets you save the purchase for future trades -- handy if you plan to stockpile games during Steam sales.
Currently only TF2 items can be traded, but Valve plans to add support for Portal 2 gear "reasonably soon," followed by various (unnamed) third-party titles over the next few months. If you want to test the new service, you can opt into the beta by opening your Steam client, clicking Steam > Settings > Change (under "Beta participation") and then select "Steam Trade Update" in the dropdown. If you experience any bugs or have feedback for the system, you can ping Valve in this forum thread.