Microsoft Research released a video called Printing Interactivity: Customizable 3D Printing. I've embedded this video below so you don't have to go find it.
In this video Microsoft is showing how they are working towards printing electronic circuit boards onto paper using a tool Like Visio. They then use a special tape from 3M to be able to tape components to what you printed. The end result is the ability to create circuits and electronic components. When you combine these printed electronics with objects you create using a 3D printer, lots of new opportunities begin to be available.
In the video, they illustrate a simple example; however, if you have messed with any of the "Maker" boards such as the Arduino or Intel Galileo, then you are already one step ahead of others in knowing the possibilities of what could be done.
Take a look at the video. Do you have any good ideas on things that could be done? Feel free to share them on the comments below!