While Nvidia has been publishing very good graphics drivers for Linux for a very long time, AMD released its graphics drivers very sporadically and often in a poor state in the past. This has changed dramatically since the release of Steam for Linux. Today, the company publishes its graphics drivers regularly with a lot of improvements and has almost caught up with the graphics drivers for Windows.
With the new Catalyst 13.4, AMD has added support for the newer Linux Kernel versions 3.7 and 3.8. For the gamers, some Team Fortress 2 and Serious Sam 3 issues have been resolved in the new version. The new graphics driver and the release notes can be found here.