Image Stabilization (IS) is a great benefit for low-light shooting. If it's in the lens it uses optical elements to minimize the effects of camera movement. If it's in the camera body it moves the sensor to achieve the same effect. It has no effect on subject motion though, so if you're shooting a moving subject at low shutter speeds, the subject will be blurred, IS or no IS.
The catch is that a photograph shot with IS will sometimes show motion blur even if the subject is stationary. The camera is most likely to be handheld (camera makers recommend against using IS if the camera is mounted on a tripod), so it's possible that the cause is a shaky camera. It's also possible that the IS mechanism itself is in motion even if the camera and subject aren't. I suspect this is because it takes a moment or two for the IS to stabilize the image. This effect is visible if IS is in the lens. If it's in the body, you can see it only if your camera has Live View.
Yet another possibility is that I don't know what I'm talking about and that every now and then I get a jumpy shutter finger. Given that I've been at this for 40 years or so, I doubt it. So my question today is, has anyone else noticed this phenomenon? If so, has it made you any less inclined to use IS? I'm on the fence. IS has delivered enough sharp photos in low light that I fully appreciate its value, yet there have been enough situations where it's done more harm than good that I don't entirely trust it. The bottom line is that I don't plan to sell my tripod any time soon.