If it is graphics related, might be nouveau driver (if you
are using an nvidia card). I had to switch to the binary
nvidia driver from
rpmfusion.org to prevent my display
from randomly freezing up (though it was just the disply,
I could still ssh into the system).
I have seen some other mysterious junk recently. My
system crashed for no obvious reason recently, then
I rebooted it again today, and got a kernel dump
on my console with a walkback saying it was in something
like "start kernel" and the stack was corrupted.
Rebooted again, no problem, ran memtest for a couple
of cycles, no errors detected.