Jefferson Han, at NYU has been working on a multi-touch screen. This is effectively a touch-screen display that is capable of detecting and tracking a large number of simultaneous finger-touches.
When used in conjunction with appropriate software, this system creates the possibility for UI designs that traditional mouse/pen interaction (which are single-touch) can not come close to.
Note that many of the demos in the video use a zooming user interface. A concept that is (IMO) made far more useable in conjunction with the multi-touch display.