Uptime: Four days, 14 hours.
After weeks of frustration, I think I have resolved the issue of my Mac Pro rebooting at random times when I tried to wake it from sleep state, most often after an overnight sleep.
Many owners of the 2008 edition of the Mac Pro have struggled with this same issue. Mac forums and even Apple's own Web site have percolated with complaints, commiserations and proposed solutions for over a month.
The most suggested remedies - resetting the PRAM and SMC (System Management Controller) have worked for a few but often prove temporary fixes. The Mac OS X 10.5.2 update had no effect.
A few Mac Pro owners returned their units to Apple, only to have the replacement unit exhibit the same problem.
An Apple Support product specialist told me to delete three power management preference files. I did. The next morning after a night of sleep, I touched the space bar and the Mac promptly rebooted instead of waking up. Not a great moment for Apple product support.
During our conversation I had mentioned to the product specialist that I was booting off a hard drive I had added to the system rather than the one that came with the Mac. He suggested I also try booting off the original drive as part of the process of narrowing down where the problem might lie (hardware or software).
After his first suggestion flopped, I tried the second. Oddly, the Mac did not reboot for the several days I ran off the original drive. In fact, the problem did not surface originally until after I installed OS X on one of my new drives and started booting from it.
Still, I had all my new software installed on the new drive. I didn't want to be stuck booting from the old drive forever. Encouraged by several posts on the forums from Mac Pro owners who'd fixed the problem by swapping drives among the four available bays, I decided to give it a try. I put my preferred boot drive in Bay 1 and the original hard drive in Bay 3. (I left my third hard drive, which I use for Time Machine, untouched in Bay 2.)
I started up the Mac Pro, zapping the PRAM for good measure (the posts in the forums suggested doing it after a drive swap.) And I haven't had the reboot-on-wake problem since.
I can't guarantee the drive swap will work for every Mac Pro owner suffering from this problem, but it should work for some. Those with just the original drive might try switching bays.
Happy as I am to have resolved the issue, I remain baffled as to why the drive swap fixed it. Does this mean the Mac Pro has an SMC firmware problem? Or is there a problem with the Mac Pro hardware itself (motherboard glitch? wonky SATA controller)?
At the very least, Apple needs to add an entry to the Knowledge Base on its Web site, so Mac Pro owners will have some information on the issue. I'd prefer a software patch eradicating the problem completely, though.
This much I do know: Apple owes the customers of its high-end Macs some sort of answer, ASAP.