PLEASE NOTE: On MacOS 10.7 and later, Apple has hidden your Library folder, so you may need to make it visible - but the location is the same for all MacOS X versions. Instructions for accessing hidden user library files: Access hidden user library files | Mac OS 10.7 Lion
If you need a quick and dirty way to restore your preferences, here's a way you can do it using a keyboard shortcut on launch:
Windows - CTRL-SHIFT-ALT immediately after you double-click the PS icon.
Macintosh - CMD-SHIFT-OPTION immediately after you double-click the PS icon.