The neatest thing about this demo isn't that 20 iPod touches have combined to make a giant touch display; the neatest thing is that the technology can scale.
Both the proof-of-concept video and the above illustration are by Japanese design house PROTOTYPE. Their giant hive display can begin a chain reaction when someone touches one iPod, or it's even possible to "drop" some items between iPods (I don't read that as full drag-and-drop capability).
Unfortunately, I have many more posts to write today, so I can't calculate the size of a 16x9 display made up of the 50 million or so iPhone/iPod touch handsets out there. But I'm sure that someone in the comments simultaneously loves maths and hates their job enough to make this numeric factoid enter our existence. [Mongoose via technabob]