The magic obesity bullet?
Ok, maybe that's taking it too far. However, there's a story in Gizmodo about an article on The Guardian. The article talks about adapting some sort of device that allows you to draw power from your body to provide juice for your PDA, cell phone, etc. Gizmodo likens this to the basic idea of the body-in-a-tube concept in the Matrix.
From The Guardian article:
"Suppose you could wear some kind of patch that drew energy from your body and converted it into a useful form to power your laptop, cellphone, iPod, GPS, PDA, Bluetooth headset, torch and sonic screwdriver? In essence, your body would just be burning additional calories. This would have to rank as one of the greatest inventions in human history and its inventor would be rich beyond the dreams of avarice. As you talk on your phone, play Tetris on your laptop or groove away to your iPod ... you'll be getting thinner."