I still get the same problem. Extreme Tux Racer segfaults as soon as i start a race. Although I haven't tried the Liqorix kernel, I am using the the mainline kernel from PPA on Xubuntu (Kernel 3.0 - 28/06/2011) and xorg-edgers PPA (libdrm, radeon, mesa, etc all updated to 23/06/2011). The crash doesn't occur with the stock libdrm/mesa/radeon/xorg and new kernel.
Another symptom that might be related is while playing Super Tux Kart and Super Tux 2 lag/freeze a lot. There is also visible corruption happening intermittently in Super Tux Kart. Once again, none of this occurs with stock libdrm/mesa/radeon/xorg and new kernel.
My card is an Integrated one (Radeon Xpress 200 RC410) if that helps.