Comment 2 for bug 138415

The same happens to me with a Radeon 9250.
When a 3d app pops up, xorg freezes.
(I must say that I experienced freezes with an ATI X600 at work, too)

My system is an updated Gutsy tribe 5.

I solved the issue downgrading to xserver-xorg-video-ati_6.6.3-2ubuntu6_i386.deb from Feisty.
So it's a regression!

Deleting xorg.conf was not useful.

Now desktop effects, games, 3D and so on, work perfectly.
No freezes anymore.

Emanuele.