Just saw on Google Video this amazing video of a 3D desktop made with the purpose to simulate a real desk.
In this prototype icons can be piled, spread all over the desk, and so on, as real books, photo or printed documents.
Here is the link of the video:
http://video.google.com/videoplay?docid=-409028730194183047and here is the link to the researcher web site
http://honeybrown.ca/Pubs/BumpTop.html