As promised, Valve is slowly but surely rolling out their inaugural release of the SteamOS that users all over can download and install, provided they are fairly well versed in Linux.
Here is what you need to get started:
Bug reporting and extras:

SteamDB notes that SteamOS seems to be based off of Debian 7.1 Wheezy. It does come with a desktop environment, one called Gnome.

The FAQ (linked above) notes that you will need the following hardware to reliably test SteamOS:
  • Intel or AMD 64-bit CPU
  • 4GB or more of memory
  • 500GB or larger HDD
  • Nvidia GPU (AMD and Intel GPU support is coming soon)
  • UEFI boot support
  • USB port

The FAQ continues on to note that updates will be automatic. Those wishing to try out other software in the SteamOS desktop environment are free to do so.

Special thanks to SteamDB for a bulk of the links and screenshots you find above. Good luck to those brave enough to test drive a nearly entirely new operating system!