SteamOS

[SealLion]

Hi folks. SteamOS has come out with an updated version for all Steam enthusiasts. It's in Beta.
A list of the distros updates includes:

upstream iceweasel browser security updates
AMD driver update to match latest released driver (14.4)
Added script to retrieve system serial number to enable hardware promo scenarios
Upstream (Debian 7.5) updates for base-files, debian-installer, lcms2, libquvi-scripts, libsoup2.4, libxml2, samba, dpkg
Added unzip, git, cgdb and rsync to the repository
Added missing SSL certificate authorities package.
Added Realtek r8168 driver.
Added support for more Intel WiFi adapters

Some information here:
Steam Community :: Group :: Steam Universe

John Vert has announced the release of an updated beta build of SteamOS 1.0, a Debian-based distribution for gaming enthusiasts that includes the Steam client and a few Steam games:

Also here:
Development Release: SteamOS 1.0 Beta Update 105 (DistroWatch.com News)

There seems to be mixed reviews from it's userbase as I try to read some of the comments from Steam HQ on it's download page.

[Sazzy]

Useable yet? First release only supported very specific graphics cards and other hardware...
A fork was created on github that supported more stuff though: Stephenson's Rocket

[SealLion]

I'd say that Stephenson's Rocket out does SteamOS by miles.

SteamOS only supports Realtek networking, or firmware-free networking. Stephenson's Rocket supports everything a modern Linux does, including WiFi.
SteamOS monopolizes drives. Stephenson's Rocket can resize NTFS partitions.
SteamOS only supports basic partitions. Stephenson's Rocket supports LVM and RAID.
SteamOS requires a Radeon 5000 or newer for ATI users. Stephenson's Rocket will use the Open Source driver instead on older cards.
SteamOS is only updated when Valve have time. Stephenson's Rocket comes with the tools to update it with the latest stuff yourself!

Funny that I never heard of Stephenson's Rocket up until now.