I am posting the first time here, so I apologize if that was mentioned already...

I activated KMS and compiled the git-versions of xorg-server, libdrm, mesa, xf86-input-ati (distribution: gentoo).

So far, all is fine, glxgears gives 1900fps (Radeon HD 4670) and I can play UT2004-demo without problems or graphical errors.

BUT: turning on the desktop effects does not work:
when using OpenGl the speed is so slow, that the system becomes unusable;
when using "XRender" I cannot use most of the effects, like snow or the desktop-switching-cube. It does not matter if I am using kernel or a 2.6.33-rcX - problem is the same.

does anybody else experience similar problems and how do you solve it?