Have this problem too on a HP nx6125 laptop with an ATI 200m with both "ati" and "radeon" as the driver. Logout creates visual garbage on the screen. Switching to a text-console creates the garbage too. System is still responsive though and i can even use the text-console to shutdown the laptop (although i don't see what i am typing).
Didn't try fglrx yet but that one is not an option for me (no sleep, hibernate and setting screen-brightness). Will provide further information if needed (dmesg, lspci, Xorg.0.log, /var/log/messages) -- Lockup problems with both the free xorg ATI driver and the proprietary fglrx driver, using various ATI cards https://launchpad.net/bugs/30447 -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
