Let Photoshop Rebuild Your Prefs
If you need to delete Photoshop's current preferences file (which is a common "first-line-of-defense" troubleshooting move), you don't have to go digging around your drive. All you have to do is hold the Command, Option, and Shift keys (PC: Control-Alt-Shift) when you first launch Photoshop, and you'll be greeted with a dialog asking you if you want to delete the Photoshop Settings File. If you do, click Yes, and Photoshop will build a new, factory-fresh set of preferences for you.
Great tip. Twittering it. Now PS just needs a way to export/backup all your prefs at once without having to track them down separately.