When I got my ATI 6950 one of the things that bugged the hell out of me was that when using iTunes, my cursor would sometimes lag for 0.1 second, then jump the distance it should have moved. Made it pretty much impossible to use iTunes without going mad on missing stuff I wanted to click.
It’s been a problem with many ATI cards and even Mac Pro with official Mac 5870 can get this with certain displays.
I searched high and low for a fix but did not find one. But today I stumbled upon the fix on Apple forums and it was quite simple, and it worked. It was simply to disable AppleUpstreamUserClient.kext. I don’t know what this kext does but I have not experienced any problems since disabling it.
Instead of having to rename it/remove it after every OSX update I made a disabler for it based on kabyl’s generic disabler kext.
Here it is:
Download GPU Mouse Fix
Note that it will not affect mouse acceleration, jittery cursor movement or anything like that, it will fix a bug where the cursor completely halts for a moment then “teleports” to it’s new location.