I too bought the stock 2.8 Octo from the Apple Store. I bought mine in Tucson, Arizona in early March 2008. I installed 8 additional gigs of RAM and two 1TB drives. I cloned the original drive to one of the new ones, placed it in bay one and wiped the original drive after verifying the new clone as good. I have my Soundsticks, HP ScanJet 5550, Griffin iMate, Logitech MX series laser mouse, the stock Apple mouse, Hollywood bridge, and the stock Apple keyboard plugged into it. I'm not sure if there's a common device amongst us, but when I read that someone had Soundsticks, I thought it may be a peripheral device causing a problem.
I've always suspected my iMate of causing problems, as I constantly ground myself on it at home and it causes a kernal panic with my PowerBook G4 (15" aluminum) when I unplug it. I love the **** out of it, and hope that I don't have to give it up.
Anyway, I had a stick of my new RAM go bad within a week on slot 3 of riser A. When the RAM went bad, I started getting restarts randomly when using Handbrake to make backups of my DVDs. Sometimes, I would get a kernal panic or just an application failure, but most of the time, it was just a restart in the middle of everything. Decided to check my new RAM and saw two sticks not registered. Swapped the sticks around the slots to narrow the bad one to slot 3, riser A. I also want to pull the stock 2GB of RAM and see if the sleep issue surfaces; maybe it is a bad lot from the factory, undetectable by hardware tests, but sensitive to something associated with sleep (i.e. low power). This doesn't cost anything to research and easy to resolve if it works.
I don't think resetting the SMC will work, as it has only worked sporadically within this group. I think I reset it when I had everything unplugged and moving the computer around, but it didn't make any difference. The PRAM reset seems like something that may work. I'll give it a try after removing the stock RAM. I think it's a hardware or possibly firmware issue.