I simply did a quick test running glxgears under valgrind (via "$ valgrind --tool=memcheck --leak-check=yes glxgears"). After only 4 glxgears "iterations" (the poor FPS are because of running under valgrind, of course) valgrind gave up for more than 10000000 detected errors and told me to "Go fix your program!"
The result is posted in the following comment (due to size constraints here). I omitted the startup output, and all those nearly identical "Invalid write of size 1"-Reports but the last one.
[Edit] This is on Lenovo Z61m / 2 GiB RAM / ATI X1400 / Gentoo AMD64 / Kernel 2.6.22 / GLIBC 2.7 / X.Org xserver 1.3 / fglrx 8.42.3
Suddenly, my hope in 8.43 just dropped like a rock.