I've been gaming in Linux with both native and Wine/CrossOver games(free year thanks to Bush) for over 8 years now. Drivers are the biggest issue. There are 2 main issues here. First is quality. The video card manufactures need to dedicate additional resources to bring the drivers up to the quality of Windows.

The second issue is with the driver subsystem. The kernel developers need either a) stop breaking the existing driver interface ever other release or b) create new modern interface that's stable like MS did with Vista.

Imagine if every windows update, you had to worry about you games not working because MS might break the drivers. This is how Linux is now. This situation is especially bad for users with old and very new cards. For example, my X1900 can't run the catalyst drivers with any modern kernel, making it useless in Linux as my spare gaming rig. Of course it works perfectly in Win7, running about 2-5x faster than the worthless, buggy, open source drivers.

Fixing the video driver subsystem is exactly the kind dedication that would prove to me that Value is serious about making Linux a competitive gaming platform and likely convince me to purchase a SteamMachine.