Well, it seems that there's a problem with System 9.04 that Apple, in a Microsoft imitation, acknowledges but won't do anything about. Now, OS X is around the corner; so I understand that the system software wizards are spread thin. But this little hummer can really bite you big time. Fortunately, there's a program out there that can cure the problem. More on that later, first the diagnosis.
The first problem sign is the gradual and inexplicable disappearance of space on a user's hard disk. This vanishing act is not always evident to a user in the era of 30-gigabyte disks; but eventually they start to notice it. Looking at the visible desktop shows the disappearance of hard disk space via the Finder's display; but all files on the desktop look and test normal. No munged B-tree stuff going on here, something that might be considered any time the Mac file system is corrupted by some incident. The Disk First Aid utility finds no problem. Desktop rebuilding does not affect the situation in any way. To make things even nastier, only some users are affected. Others report no problem with the hard drives at all; even though they are using the same system software. When you open up the hard disk's drivers with FWB's HDT toolkit --done in an act of desperation -- everything looks fine.
Quite the poser, eh?
Enough suspense. What's going on here involves the startup actions at the Mac's launch time, as well as some applications like Adobe Photoshop 6. When these programs operate, they may create invisible temporary files (stored in the invisible "Temporary Items Folder" inside the System folder). What's happening is that System 9.04 doesn't delete these files when their usefulness is outlived. The "temporary" files accumulate and eat up disk space until they can't be ignored. This also accounts for the variability of user experiences. If a user has no startup actions present (or doesn't run Photoshop 6), there would be no files to accumulate; hence, no obvious problem.
OK, what to do about it? This situation so torqued off Scott Crick, he wrote a freeware application to nuke these files. Eradicator (currently at version 1.6) allows the manual elimination of these previously invisible files. It does not do anything automatically, except it prohibits deletion of any file in use. It is a purgative for the file system, eliminating waste. It makes a sick disk well again. It's simple enough that a user can self-administer it with little fuss, and Scott made it free.
I wish all problems had this simple a solution, even though the diagnosis to get to the solution was non-obvious. Makes you feel silly for just telling that Art Director it must be something he's doing that caused his hard drive to shrink, huh?