So I've mentioned the steam Linux beta in a few threads, but now it's gone from a private beta to public which means anybody can download and use it. Valve opened up a repository (debian packages, still focusing on Ubuntu support) as well.
I theorize that Linux is going to be the OS used for the SteamBox, though not a vanilla Ubuntu. Valve seems to be putting forth more effort towards Linux than mere experimentation lately. It's likely that the Ubuntu focus for the current beta is just for ease of support, with the final OS for the SteamBox being debian-based, but with a custom/modified desktop environment.
Also of note, GitHub is being used as a bug tracker instead of just having Valve staff browse the forums for bugs.
Source
I theorize that Linux is going to be the OS used for the SteamBox, though not a vanilla Ubuntu. Valve seems to be putting forth more effort towards Linux than mere experimentation lately. It's likely that the Ubuntu focus for the current beta is just for ease of support, with the final OS for the SteamBox being debian-based, but with a custom/modified desktop environment.
Also of note, GitHub is being used as a bug tracker instead of just having Valve staff browse the forums for bugs.
The team will continue working through existing issues in the forum but it is strongly recommended that any new issues be entered using GitHub's issue tracking interface.