Today in the annals of amazing-but-completely-pointless crap you can do with an iPad: Make stuff appear in thin air!
N-3D, by Aircord Labo in Japan, is a sort of hologram machine you operate with your iPad. Set the iPad on top a pyramid-shaped box coated in holographic film, then run a multiscreen app, and poof! Phantom objects spring up before your eyes. With another app, you can even make them jump by clapping your hands. We've got the video below, though you might want to switch off your sound, unless you plan on turning your cubicle into the Love Parade.
How it works: The angles of the pyramid reflect images dancing around on your iPad. (If you want to try this at home, you won't get the same effect in a fish bowl or whatever else you have lying around.) But you can make the apps using openFrameworks and MaxMSP. For details, see here.
You might be wondering: Does this thing have any practical application beyond impressing fellow nerds at DEF CON? But, of course! As one commenter at CreativeApplications.net astutely points out: "pron will never be the same [again]."