Newsbrief: Valve has further expanded Steam's ability to handle virtual items by launching the Steam Inventory Service beta.
Developers can now use this API to create in-game items with a persistent life in the Steam ecosystem: They can be given to players in-game, and these players can then trade or sell them within the Steam Marketplace.
This comes hot on the heels of news that Steam Workshop functionality for externally-created in-game items has begun to be extended to games outside of Valve's own.
At last year's SteamDevDays Valve made a splash by discussing the monetization of Team Fortress 2 via microtransactions, which is a continued focus for the company with Dota 2. You can learn more about that from this Gamasutra community blog post.