Found this very interesting project created by Waldek Wegrzyn as part of his diploma thesis at the Akademii Sztuk Pięknych in Katowice, Poland.
The project explores, and illustrates how to use a book as a Human-Computer-Interface. It uses flexible circuits and sensors printed onto paper and hidden below the content in order to tell relevant software what page the reader is on and what they are doing with the book.
To read more about the project, see waldek-wegrzyn-paper-book-as-interface.
Also, do have a look at the Electrobiblioteka website.