I really like the idea of SteamOS - if anyone can push Linux to the "desktop" (becoming an increasingly blurred and useless description), it'll be Valve. One of the main reasons I've stuck with Windows (or at least, kept returning to it) is because of the inviability of gaming on any other platform.
After finding a couple of guides to installing SteamOS under VirtualBox, I was away. Clicking the "Steam" icon under Gnome didn't work for me, but running it from the command line did... sort of. It failed to check the update, because I'm behind a proxy.
export http_proxy=http://10.0.0.1:3128 steam
That did the trick, it's updating.