From what I've seen, Google's desktop Linux systems are just customized LTS Ubuntu images. (Source: visits to Google office) They appeared entirely normal, eg. Unity, Gnome Apps, etc. but I am sure they made some Google-specific changes.

Also, Valve released their Linux distro awhile ago. [1] And Phoronix [2] has some good Windows vs Linux gaming benchmarks. My impression was that they were getting pretty comparable.

[1] http://store.steampowered.com/steamos/ [2] http://www.phoronix.com/