Actually, it turned out not to be an OS X problem at all. I started getting weird error messages when launching the simplest of applications. The error was “The application could not be started -10810”. Huh?
Digging into it, it seemed that if I killed a few apps or restarted the Mac, it was fine for a while. It would (after a time) go back to doing what it was doing, though. I had recently moved from an older iMac to a new one via Firewire, Target Disk Mode (which is awesome), and Carbon Copy Cloner (which is also awesome and I’ve donated to the author for the fantastic software he wrote). So, I thought maybe this was the problem. I checked and double-checked and then Repaired Disk Permissions, all to no avail.
A chance meeting on Google and the Apple Support Forums led me to Microsoft Desktop (which is the Mac’s version of the IntelliPoint and IntelliType utilities for Microsoft Keyboards/Mice). Sure enough, a “ps -ax” in the Terminal turned up dozens of (MicrosoftDesktop) processes that were spawning mercilessly. Awesome.
So, I uninstalled 6.0, rebooted just to make sure it was clean, and installed the latest version (6.21) of Microsoft Desktop. Turns out the old version has a bug that seems to be fixed in this new version. Whenever your wireless mouse battery level gets low, it tries to spawn a dialog but sometimes can’t. It does this quietly over and over eating up all the available processes until your machine just grinds to a halt. So, upgrade to 6.21 (which seems to fix the problem) or change your mouse batteries.
What a blast!