More back-of-device touch interaction: Wacom's Cintiq tablet has touch-sensitive strips that let you control brush size, zooming, scrolling and canvas rotation.
I love this idea and expect we'll be seeing a lot more like it soon.
This reminds me of steering wheel radio controls. I had a 2002 Mini Cooper that had the volume and tuning rocker switches on the back of the two spokes. You couldn't see them but you could easily operate them with your fingertips while your hands were on the wheel. I think the newer Minis have all the buttons on the front. I wonder if there was a discoverability problem. Do other cars have that back-of-the-wheel design for these buttons?