So, I accidentally start World of Warcraft twice - just the launcher, not the full on game itself. Graphics card says "OMFG! NO!". The hard disk, on the same power supply cable says "Oh, you're having a problem? better tell the power management system". The power management system says "Eh... lets.. switch you both off". Graphics card says "Phew! Thanks power management!" Hard disk says "BZZT! GURK!".
Turns out, what "BZZT! GURK!" means is "Actually, I was in the middle of doing something - some automated disk maintenance of a defrag nature you *jerk*". Needless to say, the hard disk is in need of several hours of therapy and while it may walk again it is likely to suffer 100% amnesia. It therefore also goes without saying that at least forty gigs of what was on the drive was not backed up. Fingers crossed one of these tools I'm looking at can actually get the damned stuff back.