Comment 23 for bug 471872

Ok, so as expected, disabling mode setting (sudo echo options radeon modeset=0 > /etc/modprobe.d/radeon-kms.conf) did resolve my suspend issue. Unfortunately it comes with a major hit to graphics performance (e.g. Hulu is now unwatchable even in a window). Perhaps a newer kernel may resolve this issue, but for the moment it looks like you have the choice of good graphics performance and no suspend OR bad graphics performance and working suspend.