There have been plenty of interfaces that react to real objects on top of them, but PICO is another step forward due to the computer being able to move around the small magnetic pucks. This means that when you are trying to work out something that needs a blend of computational power and human sensibility, you can engage in a kind of dance with the computer’s thinking. You really need to see the PICO video to understand what I mean - it’s hard to describe in words.
Apart from the obvious practical applications of this (the example in the video is about the placement of transmission towers) there seem to be plenty of opportunities for playful interaction, gaming, art and so forth. These are by no means lost on Patten if you take a look through his portfolio. Drift is particularly nice.