Discussion
Background
The paper discusses a mobile computing system that involves projecting an interface onto the surface of the skin, and detecting "clicks" or touches by measuring vibrations radiating through the skin.
Rating
The article was a thorough investigation and examination of several skinput techniques. Of the methods described, their adoption of vibration-detection seems the most effective, although I question the system's response to accidental bumps from an outside source or natural tension in the arm muscles (as in a clenched fist). Audio-decibel filtering would be a viable workaround to these concerns, but would not be perfect. That said, however, miniature microphones sensitive enough to capture these "accidental" frequencies would be costly, and the price wouldn't likely justify the usefulness of the system.
The team was exhaustive in their testing, recruiting both men and women from outside of the lab to try the device. The system's capability to detect upwards of ten separate locations on the arm proves to be very promising for a variety of gestures and input combinations. Although the experimented on several regions of the arm and hand, I was disappointed that they neglected to test the system outside of a lighting-controlled environment. While the system would have no trouble detecting touch positioning, the user might have trouble seeing the interface in a bright or sunny environment. Though it may be ridiculous to assume the user would be interacting with this system in a sunny environment, it is certainly within the realm of possible usage scenarios. Lastly, needing to hold the arm at a specific position for projection would get tiring very quickly.
Overall, their techniques for skinput are ingenious and quite revolutionary, but application would be very limited due to so few touch positions, and environment restrictions. The most useful application of skinput would be interface-less, such as controlling a media player with finger taps.