yes I meant 1/400s
IS/VR at high shutter speeds is not only a waste of time, but can provenly reduce image quality.
IS/Vr works by having rate gyroscopic sensor measure the rotational inertial movements of the system. They have a certain sampling frequency. Most gyroscopes only do about 500Hz, but according to Thom Hogan the gyros in the VR/IS systems are 1KHZ. But Signal processing theory will explain why meaningful measurements can only be recorded from half the sampling frequency (or conversely you need to sample at twice the Nyquist frequency).
In other words, the sensors can only detect movements at a rate of around 1/500th s.
A shutter speed faster than that ballpark can lead to blur caused by the IS/VR system.
A common but not directly related example is when an IS lens is used on a solid tripod, most lenses will end up giving a very blurry mess because the system is not responding correctly to the lack of movement. (some newer lenses, especially the telephotos can detect if the lens is on a tripod or not, and then switch off).
IS/VR leads to soft images at high shutter speeds. Even at lower shutter speeds it affects image quality, often most noticeable in the Bokeh.
So in general you should have IS switched off until such time as it is needed (when you are running out of light).
Even under slower speed say, 1/200th s if you don't need IS/VR due to the focal length then it is best to switch it off. I have plenty of examples of different images that are soft and I can only assume it was the VR system making incorrect measurements.
Like any electronic sensor the gyroscopes are subject to noise and the ultarsonic motor that shifts the lens element are also subject to noise and lag. In fact the gryopes are passed through a low-pass filter to reduce some of the noise, this will further reduce the oversampling rate.
this is a good read:
http://bythom.com/nikon-vr.htm
