It’s taken a little while but the first public release of SteamOS is here.
Valve has made available two downloads of SteamOS on its website here – a default installation and a custom installation. Be careful though as both will end up completely wiping the computer on which you end up installing SteamOS.
The installation instructions can be found on the website but there could well be problems given that SteamOS is now in public beta.
I have downloaded the custom installation image but will need to find a suitable computer on which to try it on.