This problem has also been reported as https://bugs.launchpad.net/ubuntu/+source/xserver-xorg-video-ati/+bug/182430 xorg on my Thinkpad X24 has been completely broken with the gutsy upgrade. I cannot even switch to a virtual terminal with Alt+Ctrl+F1 and back to X anymore. Entering the console is fine and I can restart X or more precisely gdm from there to get back into X, but if I just use Alt+Ctrl+F7 the machine locks up completely and cannot even be ping'd anymore. I have to shut it down hard by pressing the power key for about 5 seconds. As the machine crashes, there is no way that I know of on how to collect relevant information or such things from logs. I had wondered if possibly my xorg.conf was faulty. But starting X without xorg.conf produces the same behaviour.
*** This bug has been marked as a duplicate of bug 13994 ***
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