There are satellite navigation systems for cars, why not make one for a bicycle. This amusing blog article from Japan introduces a navigation system that uses an iPhone and heads-up display unit installed on a bicycle helmet. Not the safest thing to use in traffic, especially since it affects your peripheral vision. A fun idea though.
I could do with something like this when I go mountain biking. It is very easy to get lost on the trails and it would be great to be able to easily navigate through the forests. Having the navigation system of the helmet will save it from the vibrations that handle-bar mounted systems suffer from but could be disastrous in an accident.