Yay! It looks like xserver-xorg-video-ati 1:6.6.2-0ubuntu3 fixed the problem:
* Fix radeon aperture size check that was causing hangs and crashes on RN50, M6, M7 with 8/16/32(??) MBs of VRAM: - 08_radeon_fix_aperture_size_check.diff Thanks to Ben H., Dave Airlied and Michel Danzer for their constant support. -- Fabio M. Di Nitto <[EMAIL PROTECTED]> Tue, 03 Oct 2006 09:11:47 +0200 My xrandr stress test (toggling between dual-head and clone modes many times in a row) failed to cause a freeze. -- [dapper] xrandr freezes the system (radeon, MergedFB) https://launchpad.net/bugs/47775 -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs