Earlier this year at the TED conference, Pattie Maes from the MIT Media Lab's Fluid Interfaces Group showcased a prototype of a next-generation wearable computer interface that allows people to display and interact with the Web on any surface - including the human body. The video below shows the system's main developer taking photographs with his hands, calling up Amazon review data onto the cover of a physical book, displaying information about a person he's just met on the person's t-shirt, and calling someone by inputting a phone number onto the palm of his hand.
In the presentation, Pattie Maes refers to this system as a "sixth sense" because it gives you seamless, easy access to information about objects and people you encounter. It removes several manual steps from the process of receiving relevant, contextual information. It's a MicroSoft Surface Table without the table.
The possibilities are mind-boggling. Read a great review at ReadWriteWeb.