Hi Dave, as usual reader of Arch's lists I've been following your issue and while I don't have sufficient knowledge nor enough skill with Arch to help you I second your thought the issue must reside somewhere kernel/KMS/catalyst module: currently I'm running a 64bit Arch with a ATI Radeon 5750 HD (1gb) graphic card with catalyst 10.6.5 from [Catalyst] repo without any much trouble except composite effect. With previous catalyst-test 10.4.444 everything worked fine out-of-the-box but now composite is disable on every boot so I have to manually enable it on log-in by pressing twice Shift+Alt+F12. I have had to drop old catalyst because it isn't compatible with new Xorg and recent kernel upgrade and system upgrades but I never experienced these issues with that package. Hope this help you somewhat! Martín