Product review (5 stars): Buy this part and fix it yourself.  It's not very hard at all.
If your microwave door pushbutton just pushes, but doesn't open, it's likely this thing-a-ma-bob snapped off.  Most people recommended buying a new similar microwave ($450).  That's pretty silly when an $18 part and about 30 minutes of labor fixes the problem.  There are several YouTube videos that will take you step by step through opening up your KitchenAid Microwave and replacing the part.