I have been using the old drivers for quite awhile and only updated to the Catalyst drivers recently. I have not noticed any degradation in performance with the old drivers and have noticed other improvements with them (most notably the clearing up of the artifacting in Netscape).
However, it might seem odd to some of you that, as a game developer, I haven't had much time recently to actually PLAY many games and thus, I may not be a good measure of whether anything is lost by removing the Catalyst drivers. I'm hoping some of you might let me know if you notice anything lost with the Catalyst drivers removed.
Lastly, I noticed an alarming number of issues with the Catalyst drivers when looking through the FAQ for games on the ATI web site. I'm not sure if this is commonplace, or if it reflects a problem with the drivers or with game developers, but right now I feel better to not have the Catalyst drivers loaded.
Again, I would appreciate it if people would let me know if they notice anything negative when reverting back. It will certainly help me with finding a permanent solution to this issue!
"We have found the enemy, and he is us!"