It seems that my rant regarding Apple's postponing of Leopard being a good thing (considering that Tiger has reached .9 and all) has come back with a vengeance - or a karmic reminder of how true it might actually be.
Less than 24 hours after downloading the latest Security Update, I am currently trying to figure out why my MacBook froze and, after a forced reboot, managed to not only delete all my e-mail account definitions (thank $DIVINITY for my storing everything on a home IMAP server) but also nuke the preferences for Safari, TextMate and a few other applications.
A disk error seems to be out of the question (disk checks gave OK results), but I'm betting even money on FileVault or Parallels (no, I don't keep VMs in FileVault, I'm not crazy - only my home directory is in there, VMs go under /Users/Shared).
Most of the damage seems, in fact, to be related to .plists of applications that were running at the time of the freeze. So far I have not noticed any missing data or severely misbehaving programs, and the Console is only spewing occasional complaints from Adium (which is a bit chatty in that regard anyway).
Here's a little list of useful commands to run the next time it happens (without dire results, that is):
# Enable mail bundles (for Mail Act-on and Letterbox) defaults write com.apple.mail EnableBundles -bool true defaults write com.apple.mail BundleCompatibilityVersion 2 # Enable Safari debug menu defaults write com.apple.Safari IncludeDebugMenu 1