Created attachment 518320 [details]
Kernel - 220.127.116.11-26.rc1.fc15.i686
This doesn't happen always but it did the last two times it tried to go to sleep. It seemed to hang but capslock worked on keyboard. I managed to SSH in from another system and run dmesg. The output is attached.
The latest kernel causes the system to freeze completely (another bug has been filed against it) so I can't upgrade either.
The system froze a few hours later.
That particular symptom seemed to affect a number of people in 2.6.38, (search for fault.c:1087, and you'll see a dozen or so different traces)
This one in particular looks like 708202 which I'll dupe it against.
I'm optimistic that this has been fixed in 2.6.40, so we'll focus on getting your other bug fixed asap.
*** This bug has been marked as a duplicate of bug 708202 ***