Comment 137 for bug 121653

please have a try with latest AMD/ATi drivers ver. 8.42. these seem to fix this bug.
with those shipped with Ubuntu Gutsy 7.10 I experienced this problem as well, however after upgrading I can again suspend and hibernate without any issue.

a prepacked version from ubuntu repositories is not yet available (it will be in some time) in the meantime you can download them from: http://www2.ati.com/drivers/linux/ati-driver-installer-8.42.3-x86.x86_64.run

please remember to run aticonfig --initial after installing and also that after each further kernel update you will need to re install them as far as the package will not be provided directly from ubuntu repositories.