My Thinkpad X31 laptop with a Radeon M6 graphics chip had a problem with ACPI Suspend/Resume. About every five resumes, the graphics card would get messed up, making the screen unusable.
The computer would suspend/resume fine otherwise, but I’d be forced to reboot just to get X working again. (Just shutting down X and re-starting it wasn’t enough.)

The easy solution is to pass a “nomodeset” option to the kernal upon boot, but to do this on different versions of Ubuntu you need to do modify files in different places.

9.04: Edit the /boot/grub/menu.lst file, and look for the defoptions= line. Add nomodeset to the end. Run sudo update-grub afterwards to save your changes.

9.10: Edit the /etc/grub.d/10_linux file to add a line such as:
GRUB_CMDLINE_EXTRA = "$GRUB_CMDLINE_EXTRA nomodeset"
or just add “nomodeset” to the end of a previous GRUB_CMDLINE_EXTRA entry. After this, run sudo update-grub.

10.04: Edit the /etc/defaults/grub file and change GRUB_CMDLINE_LINUX="" to
GRUB_CMDLINE_LINUX="nomodeset"
(You may have to run sudo update-grub again, or it may be taken care of for you)

Commentary: I find it funny that in each of the last three version’s of UBUNTU the name and location of the grub configuration file has changed…