I had one for a little while. I realized after I lost it that I spent all my time staring at it. It fell off one dark morning, who knows where, and I remembered one of the primary reasons I ride- to look at the world unfettered. I spent no time looking for that little digital prison, and I've been a happier cyclist ever since.

If you "listen" to your bike, it'll tell you when things are starting to wear, and might need replacement soon. You do have to listen close to hear the initial comments though! My commuter likes to have long conversations with me sometimes.