This is all due to the joys of BillOS and disk write caching. I don't pretend to understand how it works down low, but it's writing to memory in the cache and either the cache is read-only or it's flushed before the cache is written. It's the "Delayed Write Failed" thing that nobody has a real answer for. This is for every file on the 400GB disk that's acting as my storage home. Let's review: Music? Yup. I've just discovered MusikCube and I'm nowhere near the tracks I had before the last hard disk died... video? Yup. All of Doctor Who for starters. Documents? Yup. Including everything for $CURRENT_PROJECT. I'm too dumb to have checked the backups that I do have... I'm not even going to mention the NWN savegames.
Further experimentation tells me that I have a read-only hard disk. Dunno how much longer this situation will last—it's either a problem in the disk (in which case it's going straight back for replacement as it's under a year old) or it's a problem in the motherboard's SATA controller. Either way, the disk is living on borrowed time so I'm starting the DVD archiving process. Part of me hopes that it's the motherboard so that I can upgrade the machine. The rest of me notes the price of decent components and winces.
One day I'm going to take up a simple hobby where the worst thing that can go wrong is me fucking up, rather than hardware deciding that I don't need it to work before my deadline...
: I'm biting the bullet and going for a new macbook. $ORK has an employee purchase program that brings the new models within the same price range as the Core Duo ones currently on eBay. And yes, I'm getting AppleCare.