Japanese companies have implemented the Personal Area Network, using the body's conductivity to make a network between devices (PDA, phone), and person to person. IBM's PAN was six years ago, but it's still a good idea. The devil's in the details, however. Does it restrict itself to a transport layer, allowing any application to pair over it? The Bluetooth handshaking protocol would seem useful here. Does it maintain security from the ground up? And of course, for the really useful applications (like giving a select group of people - medical personel say - privy to only certain pieces of information without your countersignature), this is only one piece of the jigsaw -- we still require a massive government-funded Public Key Infrastructure to back this up (and in the UK's case to support electronic service delivery by central and local government, if they're going to meet the 2005 deadline of all services being available online).