The Preferences file records more than just the choices you've made in Photoshop's Preferences. It remembers the size of the new document you created, your last brush (for each of the painting tools), even how you left each palette. These are just some of the other things that are recorded in the Preferences file.

 

So how does it get corrupted? 

 

Keep in mind, the Preferences file is rewritten every time you quit Photoshop. One way to try to minimize the possibility of corrupting the Prefs file may be to allow sufficient time for the program to quit. Sometimes when you launch another "memory-intensive" program while you're quiting PS you can mess up the file. Some  clues that the Preferences file has gone bad are:

• Freezes and crashes.

• Unusual tool behavior.

• Menu commands unexpectedly not available.

• Missing or blacked-out icons in the Toolbox.

• Unusual colors for interface items.

 

The ultimate way to prevent corruption of the Prefs file is by making it a Read Only (Windows) or Locked (Mac) file. Remember, though, that Photoshop won't be able to update the file, so make sure that all of your preferences, palette locations, and tool settings are just as you want them before securing the Prefs file.

 

Here's a quick way to toss the Pref file:

Press down Command-Option-Shift (Mac) or Control-Alt-Shift (Windows) immediately after you start launching Photoshop. (Don't hold down the modifier keys before you launch, press them immediately afterward and hold them down until you see the dialog box.) You'll be asked if you want to delete the "Adobe Photoshop Settings File."

 

Hope this helps 

scott