Skinput vs. Sixth Sense
Seems silly to define inputs based on the sound and vibrations caused by tapping specific parts of your arm. People are fat, skinny, muscular, flabby, and so on; it seems like the variety would quickly overwhelm this system, or at least severely limit it. And from a usability standpoint, it would be extra frustrating if a button didn't give you the desired result and you knew it was your fault because you made the wrong noise with your chubby arm.
Some of the usage examples are kind of silly, but wow. I'm not too excited about all of the new augmented reality stuff happening, but sometimes I'll see something that I think might look like the future. I love TED.
Skinput via Spatial Robots