If you were to ask the average Apple fanatic exactly why the iPod had the success it did in the market, they'd probably laud the smooth white design and slim build. Not far down the list, though, we'd expect the responsive, touch-sensitive scroll wheel to pop up, an admittedly impressive feature that's been mimicked but never bettered by rivals offering similar products.

It seems as though Apple has nailed another potential generation-defining technology by patenting a design that involves a fold-out transparent panel offering touch-sensitive keys that can be operated from either side. The double-sided touchpad interface will no doubt be integrated into the iPhone, offering the advantage of a full-sized screen that won't be obscured by control buttons and other operational elements.

It's certainly an intriguing idea, and although some users may claim that there's nothing wrong with the stylus approach taken by most PDAs, we think that if anyone can take a quirky idea like this and find a way to make it an invaluable aide to consumers, it's Apple.