While this is great, its a bit sad that Valve is mostly doing all of this now, because they fear losing their dominance on windows to the native Store in Win 8.x In the end its a win-win for everyone if it works out, just their motives are questionable.
Then I heard how performance issues. Using games performed (slightly?) better on Linux then on Windows. There was talk about mouse issues on Windows 8 and how some bench marks could be faked.
All this sounded to me was Valve wanted a better gaming environment.
Side note, I don't know how many people would be switching to Windows' store and gaming social features over Steam.