I expect I know what the answer is, but never hurts to ask. A good friend of mine has a 20" iMac (1st gen aluminum) that's been struck dead with a corrupt hard drive directory twice lately, and I'm trying to figure out if it's just incredibly bad luck or there's a root cause I'm not seeing. He was previously running 10.5, when his computer started acting up badly, until it eventually wouldn't even boot. I checked it out, and the hard drive was corrupt to the point fsck and even TechToolPro 4 couldn't fix it. I did eventually get it to mount read-only, so I got the files transferred off, though, so I wiped the drive, installed Snow Leopard, and use Migration Assistant to get things back to where they started. TTP said the hardware was fine, and after updating all his software and adding a 2GB stick of RAM everything seemed to be running fine. Then, a few weeks later, something went horribly wrong (I think he said during an attempt to update to 10.6.2). Again wouldn't boot, and again severe disk corruption--"Keys out of order". This time after a lot of coaxing I got TTP5 to rebuild the directory, at which point Disk Utility did about a dozen passes fixing one thing after another before finally declaring the drive ok, minus a few damaged files and with a few things in a new lost+found folder. I mounted it via target disk mode, cloned the drive to a disk image with CCC (clone went fine), zeroed the drive, reinstalled 10.6, updated to 10.6.2 etc, Migrated everything back over, and again it seems to be running fine. But given how rare corruption that severe is on a Journaled drive, I'm wondering if there's not a root cause that I'm missing. A full bad block scan with TTP came up clean, as did all other hardware tests, and letting Rember (memtest) run all night (11 passes) stressing the RAM also came up with a clean bill of health, so it at least doesn't seem to be hardware. The only peripheral is an ancient HP printer. The only system-level stuff he has installed is a Wacom tablet driver (and maybe an older Canon scanner driver, but I think that runs in the user space, and I doubt it's a problem anyway since I was using the same scanner at one point without issue). Software appears to be mainly WoW, Sketchup, Blender, and Limewire. None of which seem to be suspect in terms of disk corruption, to my knowledge. Anybody have any guesses or anything else I should try/check before I hand it back to him?