Linux

[ScapeZero]

Don't worry, that number is going to go up dramatically when Steam is out on unix.

Doubt it. Games will still run better in DirectX, much like how most people will use Bootcamp when running games on Macs, simply because they get better performance than running the game on OSX.

Not to mention, most developers will not make Linux ports of their games. There are very very very very few games that run on OSX on Steam (and in general). Its mostly just indie games that run on something like Flash, and then Valves own titles.