Steam Trading, which allows Steam users to exchange in-game items and Steam Gifts with other members of the community, is now officially live.
The Steam Trading beta that launched back in August must have gone awfully smoothly because here we are, less than a month later, and the program is out of the gate and moving at full speed ahead. All members of the Steam community now have an "Item Inventory" in their user profiles that tracks all the items they've earned or purchased that are eligible for trade. It's currently limited to in-game items from Team Fortress 2, Portal 2 and the co-op adventure game Spiral Knights, as well as gifted games that haven't yet been accepted, but virtual items can be traded with other gamers from anywhere else in the world, with no regional restrictions.
Nothing of note appears to have changed from the beta version of the program: gift games and extra copies can be traded but used games cannot, so once you open your gift and add it to your library, you're stuck with it forever. The trading program is also very much a "caveat emptor" affair, as reported scammers will be punished but any items lost in a scam are gone forever.
More than one million TF2 in-game items and Gifts were traded over the month-long beta period and Valve said that it's working with other developers to incorporate inventories and trading into their games, with announcements about future trading-compatible titles expected over the coming months. In the meantime, more information about Steam Trading can be found at the Steam Trading FAQ and Steam Trading Policy page.