From the "Really, Really Neat Hacks" Department: someone figured out how to make an iPhone and a Nintendo Wii controller (the so-called "Wiimote") exchange data over a Bluetooth connection.
They then crufted together an iPhone app that displays the motion and orientation of the Wiimote, in virtually real time. Observe:
And just as the Bluetooth connection is bidirectional, the usages of this hack are twofold: either a Wiimote can be used to control an iPhone app, or the iPhone can sub for the Wiimote and add another pop-up tool to its "Swiss Army chainsaw" reputation.
[Via Make Magazine]