I did my normal update recently, and then my suspend stopped working. The first suspend *would* work, but then the next one would disable the screen, spin down the disks, but then start up again straight away (but with the screen still off) forcing a reboot.
The line that was failing the the pm-suspend script was
/usr/lib/pm-utils/pm-functions: line 297: echo: write error: Device or resource busy
When I downgraded the kernel back to linux-3.4.7-1-x86_64 and suspend started working repeatably again.