Noticed the cyclometer on my commuting bike was flapping around, so I finally checked it out. Damn thing vibrated itself apart from the mount, so I had to take it off (not sure I'll replace it ... who cares how fast I'm going on my commute?).
I've only been using it a couple of years or so, but look at the mileage.
Now I know why my car doesn't pile on the miles very fast.