[Microsoft TechFest 2008] Patrick Baudisch gave me a demo of the LucidTouch prototype that he is developing with his colleagues from Microsoft Research. Instead of the regular touch screen experience of the iPhone, the LucidTouch enables people to browse a map by touching the back of the device and seeing theirs fingers as a translucent overlay on top of the graphics that they are navigating. It prevents the fingers from occluding the graphic elements users are browsing, it would be useful for small screens.
The prototype (photo) is bulky and not very practical, the Web cam located on the back make it even worse, but we can imagine better designs for future mobile devices using this concept. According to Patrick, a possible application could be a watch that users could browse by touching the watchband with one finger on the other side of the wrist.