I'd be curious to see if anyone using an SSD for their OS and apps gets this also... Apart from more memory, this issue is making me more and more want to get an SSD.
Ran the extended hardware test (>2 hours) by pressing D and holding down till EHD screen comes up on startup. 4HDD/11/40000004: SATA(0,0) error. So if you're having some issues, and you've run Disk Utility all the parts, you might just want to run EHD after sorting out PRAM etc.