An interesting concept by this japanese team Prototype linking up 20 iPod Touches using a custom application to sync them together. Considering the price of an iPod touch, it does make is a pretty affordable multi-touch (mobile computer) display. Used in array with other touches running custom software, stripped off their corporate skin (ie remove outer enclosure), could result in some very interesting installation pieces. See movie clip below + proposal diagrams showing a very large number of them.
more on the iPod Touch Cluster