hello there.
i have been having this problem since the last couple of months.
something happened or i installed something that is making gdm crash/freeze after the second suspend/resume job. the first one usually works. i have been reading other forums and most of them talk about a real issue on this topic going on for gnome 3, but never for gnome 2.

actually i never had this issue before, it was rock solid and i could put the laptop to sleep 8-10 times in a row with no problems. i have been reading about pm-utils, pm-suspend.log, about virtualbox process probably freezing the graphical desktop and i can't find a solution. when i go to pm-suspend.log apparently everything is going fine after resume.

as i said, everything was working fine before, even with screen-saver password. then i removed the password option, and it did not work either. basically what it happens is, that my graphical desktop crashes and i can only see my mouse moving but the whole screen frozen. i am suspicious of three possibilities: graphics drivers, firefox & something else.

since i own a hybrid video laptop, i had no problems with bumblebee in the past; and usually when the screen freezes, firefox is running with a high cpu%. it cannot be blamed all on firefox since sometimes it freezes even when it is not running.

i am able to return to the graphical desktop by doing ctrl+alt+backspace to kill gdm and re-login again. the problem is, that i lose everything i was doing; or by going to text mode ctrl+alt+[1-6] and typing as root: $reboot since i don't know another command to replace the gnome shell, other than ctrl+alt+backspace.

my specs:
dell xps l502x laptop
4gb ram
500hd hdd
sled11sp4 with all updates applied

i am going to try to reproduce the problem by going back to sled11sp3 to see if i am able to experience this problem again.
if you have dealt with this problem before and found a solution, let me know.

i'll share my results if i find something.