It's hard enough to look at your GPS and at the road while you're driving, but on a bike that split second of inattention could easily lead to injury. So Dutch researchers, who know from biking, have developed a music-based navigation system called "Oh Music, Where Art Thou?" It's a smartphone app that lets you navigate by following a strain of music through the streets. If the sound seems to come from the right, you go right; if it comes from the left, you go left. (Hopefully there's a needle-scratch feature for missing your turn.)
Does it work? In the tests shown here, it seems to, especially if you don't mind strapping your phone to your head and looking like a dick.
Now, there are a few obvious problems with this. First, it works best with headphones (though if you play the concept video, top, without them, you'll see that you can still basically tell where the sound is coming from). It's not really safe to listen to headphones on a bike, although lord knows people do it anyway. Perhaps someone can build a speaker into a helmet?
Second, as long as you're wearing headphones, it's not clear why the voice instruction part of GPS ("in 500 feet, turn left") wouldn't work to get you where you need to go. Still, listening to music wafting from side to side sounds a lot more pleasant than hearing your GPS governess bark instructions. Although the concept video music seems to sound like the Last of the Mohicans soundtrack, which is not to all tastes.