Matt Yglesias is hoping that one day we'll stick an RFID chip in our forearm and stop having to carry around so many keys and shopping cards. Given privacy concerns and the fact that surgery is expensive and not exactly the most pleasant experience in the world, it's more likely we'll come up with an alternative. But, what could that alternative be? We'd need some sort of device with a modest amount of computing power, capable of sending and receiving signals, that people are almost always carrying, and that's capable of some sort of near field communication. If people had such a device, they could use it to interact with grocery store kiosks, car doors, and the like.
... nope, not coming up with anything.