Valve has announced a new beta today, this time for Steam Broadcasting.
Starting today Steam gamers may watch their friends' games through the click of a button via Steam Broadcasting, now available in beta.

Steam Broadcast is designed for ease of use, allowing anyone to view a friend's game by simply clicking on "Watch Game" on their Friend's profile or Friend's List to open a window into their gameplay - no game ownership, special fees, or additional apps required. The beta is open to everyone who opts in to the Steam Client Beta (via the Steam Settings panel), however bandwidth may be limited during the beta.

This handy FAQ and information page for Steam Broadcasting should tell you everything you wanted to know about the new service. You do have total control over who can and cannot watch you play your games thanks to a variety of privacy settings. If you allow your friends to watch, broadcasting automatically starts when they click to start watching.

The beta is now underway. All you need to do is let Steam updated to the latest beta client and you are good to go.