Been on the road a lot since my comments on Sept 27 so I hadn't touched my MacPro until last weekend. Unfortunately my Mac still is unwakable once it goes into sleep mode. I tried adjusting the Energy Saver settings, un-checking the "Put hard disks to sleep whenever possible", but this did nothing. I've also tried other suggestions in this and other threads, like using the F1 or Brightness key to wake it but none of these has worked.
Again, my configuration is: Mac Pro - Early 2009, 2.66 Quad-Core Xeon, 8 GB DDR 3, NVIDIA GeForce GT 120 512 MB. 4 internal hard disks, 2 attached external drives (1 USB + 1 Firewire 800) for backup. Running 10.8.2 with all indicated software updates installed.
I also have a MacBook Pro Retina, Mid 2012 running 10.8.2 that wakes from sleep just fine. I checked the Energy Saver settings and noticed that I had set "Computer Sleep" to "Never" at some point. There was a comment in one of the other threads that indicated that this setting had fixed the sleep problem for them. So I plan to try this setting on my MacPro tonight and see if it enables it to wake. I will report back.