Quite tricky to illustrate this one with pictures, so you'll just have to read my lovely words and concentrate. Apple have filed a patent whereby the rear of a device responds to touch control whilst the front of it displays the output; kind of like unhooking a ladies bra while standing in front of her, if that makes it any easier to visualise.
Imagine an iPod-like device where the scrollwheel has been placed on the back panel - you run your finger around it without actually looking at where your finger is. Alternatively, the controls could be split between front and back, with the scroll operated in the traditional way but, rather than then moving your finger to the centre button, you click to select using a touch-sensitive button on the rear.
It becomes a little clearer if you think of the oft-rumoured widescreen video iPod, as a potential interface that would avoid smudges across the screen. In such a device the controls would be far more straightforward than on an iPhone, so it would be easy to track an engraved scrollwheel on the back without needing to see it. It would allow for the device to maintain the shape and size of a normal iPod, but with a far larger screen occupying one whole face and without the need for a standard touchscreen.
Of course, patents are inevitably obscure and vague as to application, and this one is no different. Needless to say, though, if you thought Apple were putting all their control eggs in one capacitative touchscreen basket, think again.