For my first experiment with Processing and Arduino, I'd like to make an interactive wallpaper. People walking across the wall would determine the speed and direction in which the wallpaper would be pushed. As the wallpaper is pushed, the pattern of the wallpaper changes slightly, and is affected by the velocity of the movement.
The Barbarian Group Grass Wall
Transit by Scott Snibbe (2010) LAX Airport Installation: Note the 'wiping' method in this project