Finally. I've been looking forward to this, and just happen to have a spare quad core AMD box with a GTX460 sitting in it to play around with this on. Hopefully being able to boot right into the Steam Big Picture Mode will be possible, then you'll rarely ever need anything other than a gamepad to move around the interface and launch games.
Anyone have any plans to build a gaming PC specifically for their home theater just for this purpose? I don't see myself using my main gaming rig for it since I like to sit at my desk and play as well, but having a "console" PC to play Steam games could be potentially awesome.