I feel like motion blur should be used like mouse acceleration. Like you said: If I whip my head around quickly that image should present clearly and immediately. However, if I'm in a car or flying through the air (in a game) this may distort the image as I'm glancing. This is the kind of drag-as-you-accelerate blur I'm expecting, and it can really make a fast-paced moment look that much more exciting. Motion blur is poorly executed everywhere.