There is no question that you can print a lot of fun things with a decent 3D printer. Some folks have used their 3D printers to build useful tools to use around the house. Take this 3D Printed Automatic Pet Feeder for instance. It is developed to dispense dry kibble in one cup increments two times a day. The feeding times and number of increments are adjustable, so the pet feeder works for small and larger dogs.
The housing, cylinder, funnels, and other parts are 3D printed. The developer also used an Arduino Uno R3, a sensor, and a few other parts to complete the project. You can find out more about this pet feeder on Instructables.