There's little doubt that people see value in digitally-obtained objects. "World of WarCraft" items can sell for hundreds of dollars and people have marathoned dozens of matches of "Team Fortress 2" in the hopes of obtaining a really fancy hat. Valve has added more value to those items in their own games by allowing people to trade within the same game. For example, one "Team Fortress 2" hat for another. The value of that fancy hat is about to go up even higher now that Valve has introduced Steam Trading, which officially launched today.
Steam Trading allows players to trade in-game items for gifted games through Steam, while also allowing for in-game items in one title to be traded for in-game items in another. For example, a fancy hat in "Portal 2" for a pretty hat in "Spiral Knights." Being able to trade giftable games is definitely the most intriguing part of this, as you could basically earn yourself a copy of "Portal 2" just by finding a unique weapon in "Team Fortress 2" that someone really, really wants.
Also interesting is the concept of a universal inventory, which will allow you to share inventory space across multiple games, almost like a universal stash of virtual goods. Right now the universal inventory is supported through Steam but soon you may start seeing more games that support it right through their menus.
It does beg the question of whether all of this digital item trading is a hindrance to the art design of the games themselves. "Team Fortress 2" was once a pretty uniform game, but now there's really no telling what sort of wacky hat-wearing foe you might get whacked by.