Much has been said about streaming from a Windows PC to SteamOS , but that functionality is available on other OSes , and fully integrated with Steam as of today. Let the Steam client update, and you can now stream a game running on a Windows PC to another Windows PC, a Linux PC, or a Mac on the same network, with "support for more systems coming soon." I tried streaming between two Windows PCs on our office network, and wouldn't you know it, it worked swimmingly.
Since I had been playing it yesterday, I launched Wolfenstein: The New Order on the LPC , walked to my desk PC, selected it in my Steam library, and the option to stream it replaced the option to install it. A couple seconds later, I was looking at Wolfenstein's menu.
At first, I was concerned by mouse lag in the menu. I'm using a 1920x1080 monitor at my desk, but the LPC is running Wolfenstein at 1440p—more than network lag, that downsampling was probably causing my mouse movements to feel sluggish. I turned up the sensitivity and it felt better, and when I started playing I barely noticed that my input was being sent across the room.
Next, I tested a few games which require more precise input, this time going the other direction—streaming from my slightly more modest desktop (Core i7-990X, Radeon HD 5970) to the unnecessarily powerful LPC. Nidhogg seemed like a reasonable benchmark, and after playing remotely for 15 minutes, I couldn't attribute any of my failures to input lag. I also tried TowerFall: Ascension, and even had a good run in Super Meat Boy.
Your success will vary depending on the quality of your network and the systems you're streaming to and from—I don't recommend trying to enjoy Grid 2 by streaming it from a laptop with an integrated GPU to a three-year-old netbook. I also wouldn't stream a competitive shooter, where every millisecond counts, but I can't think of a good reason to want to compromise there in the first place.
SteamOS is a lovely idea—I'm all for challenging our dependence on Windows—but if you just want your Steam library on your TV without buying a second full-power gaming rig, you don't need a new OS. The simplest approach is to connect a dated Windows machine to your TV, launch Steam in Big Picture mode, and stream games from your usual gaming rig. We'll follow-up this anecdotal test with more precise measurements in the future.