Valve has confirmed that it's working on console-like PCs for the living room. The systems will run Steam on top of Linux, and you can get a taste of what's in store today. Valve has opened the doors to its previously closed Steam for Linux beta.
To celebrate the open beta, Valve has released an updated Steam client for Linux. Anyone can download the new release, which tweaks the Big Picture interface designed for navigating from the couch. The latest client also fixes bugs associated with Team Fortress 2 and Cubeman.
If you're aren't running Linux but want to check it out, Valve seems to recommend using Ubuntu 12.04, which can be downloaded here. The Ubuntu Wiki even has instructions explaining how to install the Steam client. The same page also provides details on how to update AMD, Nvidia, and Intel graphics drivers—something you'll want to do before trying to play games.
Speaking of games, searching the Steam store for Linux-compatible titles reveals 36 offerings. Most are more casual titles from independent developers, but Team Fortress 2 and Serious Sam: BFE are both on the list. Valve is working on a Linux port of Left 4 Dead 2, as well, but that game isn't available just yet.