Valve is working to get Steam on Linux, and the first game for it, Left 4 Dead 2, already runs faster than the Windows version.
An update on the Valve Linux blog details everything the team has accomplished so far to make Steam and L4D2 a reality on Linux. When Valve first started on the project, L4D2 ran at 6 FPS. Fast forward to today and now Left 4 Dead 2 is at 315 FPS, while the Windows baseline is at 270.6 FPS using an Intel Core i7 3930K, NVIDIA GeForce GTX 680, and 32GB of RAM. The studio was able to accomplish this feat by modifying L4D2 to work better with the kernel and OpenGL, plus by optimizing the graphics driver. Coincidentally, these enhancements allowed the Windows version to perform better, although it only manages 303.4 FPS.
Valve is using the 32-bit version Ubuntu 12.04 for now, but will change to 64-bit later on. It is still fascinating to see an OpenGL version of L4D2 run faster than the Direct3D version for Windows, but that begs the question of how is that possible? The developer did some analysis and determined there are a few additional microseconds per overhead batch for Direct3D compared to OpenGL, which affects performance in Windows. They're working to address that issue, so who knows, maybe L4D2 on Windows will match the Linux performance.
Valve is also working with AMD, NVIDIA, and Intel to make sure all the graphics drivers behave under Linux. Engineers from those companies are working on-site with its engineers, so any bugs that appear can be easily squashed. The entire Linux community should benefit from these improvements, and should go a long ways toward establishing Linux as a viable gaming platform.