Recently I installed Ubuntu 12.04.1 on my laptop with an ATI Radeon HD 5450.
The open-source drivers perform well for the desktop environment, but not so with games. I just switched because I thought I would be able to play some simple games with the recent progress in gaming on Linux (Steam, HiB...).
So as Steam suggested, I installed (via Steam) the latest beta drivers. My card was not yet supported. So I installed the main fglrx via jockey. This one also did also not perform well.
At last, I updated to Ubuntu 12.10 to be sure that I had the latest packages (xorg and such), and then I installed the 13.1 drivers manually according to this guide.
The game I measured the performance with is Xonotic, a first person shooter. The first time I started it I got >100 FPS, which was equal to the performance on Windows. But after loading a second map the framerate got down to 10-30 FPS... after closing the game this was also noticeable in the desktop environment, everything went slow.
A reboot does not solve the issue, sometimes I get full performance, and most of the times it's slow.
I already tried customizing options in the Catalyst Control Center, but it doesn't make any difference.
Is there someone out there who also has this problem? And maybe someone who knows how to solve it too? :P Thanks in advance.