I've had to tighten the screw a few times on my Cygolite mount (on my main commuter bike), but no more than a couple of times per year. It never gets to the point where it's just flopping around, but sometimes it will loosen to the point where a solid hit from a crack or hole in the road will make the light shift slightly. So I just snug it down and it's good for another 6 months or so.