What concerns me about SteamOS is their (supposed, as I don't know if it's been actually confirmed yet) Ubuntu base. I personally loathe Ubuntu, it and all its derivatives seem bloated and unstable, I get the same feeling using it as I would get using Windows Vista. Remember the extra hoops Vista introduced to get to basic network settings?
Ubuntu might be Open Source, but it's not open, user-friendliness should not equate locking down an OS, there must be -and is- a better way. I feel GNOME on my Arch install does the job admirably, so much so that friends want a piece of the action.