An issue in xorg-server-core, that slows down the 3d performance of proprietary drivers from ati still exists in Ubuntu 10.04 release,and the previous bug fix don’t work on Lucid any more.

Here is a patch posted by felix kuehling to fix the problem and following is howto put the patch on your system.

open terminal from Applications->Accessories menu and type this to add PPA:

sudo add-apt-repository ppa:info-g-com/xserver-xorg-1.7.6-gc 

then,update and upgrade your system:

sudo apt-get update
sudo apt-get upgrade

Done.Hope this could help!
Check this bug at: