Never had this issue, but what I would do in your case is to move /Library/Preferences folder :
- As you made an update to 10.8, system files have been replaced so it's not a system coruption.
- As you have this problem on 2 separate users, it's not a homedir or account problem.
Try to boot in single mode, (cmd s) then mount the drive (mount -uw /) then rename the Preferences folder (mv /Library/Preferences /Library/Preferences.old) then reboot (reboot)
If it doesn't solve the problem, backup your data, format the drive, reinstall the system and applications and then restore your home dir