don't save shortcut
Seven years I have been using Mac OS X, and this entire time I have hated moving my hand to the mouse to select the “Don’t Save” button on exit dialog menus.
Well, I finally looked up the shortcut and then I promptly forgot it. This time, I am writing it down. Here it is, and I hope it helps.
Command-D
Selects "Don't Save" in dialogs that contain a Don't Save button, in Mac OS X v10.6.8 and earlier
Command-Delete
Selects "Don't Save" in dialogs that contain a Don't Save button, in OS X Lion and Mountain Lion