The Steam game 'Left 4 Dead 2' is generally laggy, and basically unplayable. I'm upgrading from an Nvidia GeForce GT 240, and there was previously no lag. Now, looking around in the game feels very 'heavy'. The visuals lag in general about a quarter of a second behind the input, fluctuating slightly. There is also occasional video and audio skipping, especially during the opening map videos. I am using the current stable AMD driver for Ubuntu.
Regardless, thank you AMD Linux team, for your attention on improving drivers for other Steam games.
Ubuntu 12.04.4, 64-bit
Unity Desktop Environment (vanilla)
Asus M4A78LT-M LE Motherboard
Asus BIOS Version 0803
AMD Athlon II X4 645, 3.10 GHz
AMD Radeon HD 6790
Catalyst Control Center Version 2.20
ATI/AMD Proprietary FGLRX Graphics Driver (Post-Release Updates)