The door to my garage doesn't have one of those elf doors or a potted plant or concrete gnome. A couple of years ago I acquired a dead G4 tower, the model affectionately termed "mirrored drive door G4." After gutting it down to the fan and a few cables, I set it outside my door. Why? Sometimes I'm carrying an arm load of items and have to set something down to unlock the door. This tower table is the perfect height to sit a glass of water down while I get my keys. Notice how the mirror finish, even after years of exposure to the elements, is still pristine.
Have you seen any old Macs pulling odd duty? Aside from aquariums, of course.