Using conductive paints and the "paper" arduino, mechanical engineering student Jie Qi created this lovely interactive electronic pop-up book that illuminates and plays sounds.
Jie Qi used conductive and resistive paint on each pop-up page. The silver traces are water-based conductive paint that contain copper powder while the black traces are the resistive paint.
Personally, I love the sound and interaction of the magnetic power source and "paper" arduino circuit board that snaps into place. (Littlebits also uses magnets as connection points).
As demonstrated in the videos, Jie Qi created a set of novel switches and controls using paper, conductive fabric, conductive paint and resistive paint. One example is a simple tact switch made by connecting one conductive fabric patch to ground and a separate patch to the input. When the user touches both patches, the input goes low. Capacitive touch sensing was also employed to control the electronics.