So Valve are going with their own OS. I think it's a interesting move but i'm not sure its the right one.
Still if they push it hard enough it might work. I'm guessing it's going to be a skinned Linux (probably based off Ubuntu).
It'll be interesting to see what they do about graphics driver support. Thats usually a bug bear of many linux gamers although the quality of them have come a lone way in recent years.
Also they have released an image of their new controller design:
It looks weird to say the least! Again it's a bit of risk as PC gaming is designed around a keyboard mouse combo.