Apple preferences discarded

Question

A preoccupying disease occurred 2 times last month and a couple before, one to my Quad and one to my friend's PMG5 2x2.0:
both machines have multiple accounts, one for administrative purposes and one for work (each account is able to Administrate, btw) and fast switching from one to another never brought a problem but recently, after a logout from an account or after a restart all preferences related to Mac OS X applications (Finder, Mail, Dock, Preview) simply vanished reverting all the settings as the first time run.
Only one account was effected.
Other apps such Photoshop or Graphic Converter (for example) kept their preferences and still work fine.
Finder view preferences, Safari bookmarks, iMovie settings and last opened project, Preview settings... all reverted to factory since in the preference folder there was no trace of related documents until the application got opened and created a "new" one.
In the Dock all icons placed by user disappeared and in place for iMovie or Garageband (two among many others) were grey "question marks" as the applications ware missing. (both iMovie and GB were right in place in the Apps folder).
As usual, repaired privileges and ran Disk Utility from the installation DVD but no errors were found.
Anyone encountered this problem more than me? Solutions?

Answer 1

Exact same thing happened to me. First symptom (before restarting) was my wallpaper reverted to the default and my screensaver did likewise. Both refused to be changed from their settings. After restart, all factory settings including dock contents, etc. were active. Start at logon applications failed to load.
I reset them, restarted, and it reverted again.
Other apps preferences unaffected
2 accounts; one administrative, one clean
G5 running Tiger 10.4.9