The change-log with the AMD Linux driver download link can be found here. "AMD Catalyst 12.11 Beta 8 for Linux includes significant performance improvements for Left for Dead 2."
The main change, of course, is the L4D2 performance improvement. Phoronix benchmarks to be conducted in the next few days will also to see if these are broad OpenGL Linux performance improvements or just isolated to the Valve games running on the Source Engine.
Stay tuned for more information as the Valve Linux push begins to intensify.