OK, seems I condemned the driver to early in the other thread. The screen corruption seems to have been triggered by the doom3 demo; the weird thing is that it persisted even over a cold reboot! My other issues were results of incorrect libGL symlinks (slap myself, I should be using linux long enough to be aware of stuff like this).
The only other remaining real issue for now (didn't test aiglx) are the dysfunctionality of driconf, but now that amdcccle works, this is not an issue anymore.
My machine is a Thinpad T60, X1300 mobility, Core Due (NO Core2), gentoo stable, kernel 2.6.20, xorg-server 1.2