The folks at InformationWeek have a report about Microsoft researchers developing a new mobile platform called LucidTouch; if that is true, it would be revolutionary.
[Microsoft is] developing a mobile platform with a touch screen system that is double-sided and appears transparent, allowing users to manipulate content with their thumbs and fingers wrapped around the device.
User interaction occurs via touching either the front or the back of the device. To allow users to accurately acquire targets when utilizing the back though, a feature called pseudo-transparency creates an on-screen silhouette of fingers that is wrapped around the back. This has the effect of easing navigation.According to Microsoft researcher Patrick Baudisch, users found touching the back preferably due to "reduced occlusion, higher precision, and the ability to make multi-finger input." (Bold emphasis mine) As can be expected, there is no release date for the device. It would appear from the photos that the prototypes are being co-developed by HP's Compaq division, who in the past were involved in designing the Tablet PCs with Microsoft.