I am running fglrx 9.2 on a 4850 card with openSUSE 11.1 and KDE 4.2.2. Whenever a window thumbnail preview (e.g. in the taskbar or with the Apple-Expose-like effect) is shown, I only see a black rectangle as a thumbnail instead of the window content.
Am I missing e.g. any xorg.conf settings or is this a known limitation?
In System Settings->Desktop->Desktop Effects->Advanced, choose "Bilinear" as Texture Filter. fglrx doesn't support "Trilinear" with KDE 4 (or perhaps it's a bug in KDE rather than fglrx, I don't know) resulting in the behavior you described.