Sony's US Patent application 20060099808 describes an "electrorheological fluid device and an electronic apparatus, which realize satisfactorily changeable hardness or tension in a portion of the device or apparatus which a human body touches, enabling application to a product that needs to have portability."
Basically, the patent describes electronic devices and displays that are flexible enough to be rolled up or folded when not in use, but become rigid when a small electric current is passed through them. The application lists wide-ranging uses for the technology, and suggests it could be applied to cell phones, PDAs, PCs, remote controls, clocks, glasses, and even game systems.
"The electrorheological fluid device can be applied to, for example, part of a controller of a home-use game machine as another example of the electronic apparatus of the present invention. A user touches a control section of the controller by fingers, and the feeling of touch is controlled by the electrorheological fluid device. For example, if a game player is defeated in a fighting game, the electrorheological fluid device is controlled to become soft in order to improve the realistic sensations in the game."
As of press time, Sony representatives had not responded to requests for comment on the patent's planned uses.