Valve is working hard on the Left 4 Dead 2 port for Linux and they are trying to make it run beautifully on it, especially on Ubuntu 12.04 LTS 32-bit.
The hardware used by Valve for testing Left 4 Dead 2 is in the high-end range: Intel Core i7 3930k, NVIDIA GeForce GTX 680, and 32 GB RAM. The software used in the tests was: Windows 7 Service Pack 1 64-bit, Left 4 Dead 2, and Ubuntu 12.04 32-bit.
There are a lot of interesting numbers mentioned by Valve in their announcement, but one caught our eye, regarding the performance of OpenGL and Direct 3D. "This experience lead to the question: why does an OpenGL version of our game run faster than Direct3D on Windows 7?"
"We have been doing some fairly close analysis and it comes down to a few additional microseconds overhead per batch in Direct3D which does not affect OpenGL on Windows” -
was stated in the blog announcement
We are now waiting with great interest the Steam client and other Linux gaming news from Valve!