Combined with an eyetracker- and some more subtle head motions- it could finally give a computer game style interface for wearables!
Want to turn on your wearable's WiFi? Look at the WiFi logo on the screen and waggle your ears a couple of times! Much easier and more hands-free than either press-button on your arm or bring up a two-hand virtual display.
Also, don't like certain people? Upload a different config file to their MP3 players. Have them stick their tongues out to turn off their music. "HEY, TURN OFF THAT DAMN RACKET!"*sticks tongue out* *wakes up in intensive care*