Just installed Kubuntu 10.10 on my old ThinkPad T43p. It has an ATI FireGL V3200, which is similar to the Radeon X600. The latest fglrx driver doesn’t support this card anymore, however the open-source ‘radeon’ driver does. The driver is enabled by default in a fresh install of Kubuntu maverick, however KDE desktop effects are not enabled. After some research, I found that “KWin has detected that your OpenGL library is unsafe to use, falling back to XRender.”
The solution then is to force Kwin to enable desktop effects and stop complaining.
Thanks to Rog131 of kubuntu forums.