SteamOS is a Debian-based distribution designed to be the primary operating system for the Steam Machine game consoles.
Ranked in these QuestionsQuestion Ranking
Pro Streaming service integration (under development)
Valve is in talks with streaming companies such as Spotify and Netflix to bring their features to SteamOS.
Pro Native graphics processor support
The OS natively supports Nvidia, Intel, and AMD graphics processors.
Pro For entertainment, it just works
What media center software do for videos, it does for games (and later videos).
Con Not built around the desktop experience
SteamOS is, first and foremost, meant to act as a gaming console - it doesn't ship with even some of the most basic applications, such as a file manager or image viewer. As a result, using SteamOS as your primary operating system would require a fair bit of work.
Con Hard to install
If you've installed Arch you're probably fine, but for those used to simple installs like (Ubuntu to name just one) you should prepare some patience, determination, and painkillers. Good news is, it's getting better (it's very young).