Good to hear of your positive experience RMWD.
It's a contentious issue. However some evidence is certainly out there and can be found with some judicious Googling, there are plenty of owners with the opposite experience to your own. It really depends where in the cycle the shutter operates but when people such as Thom Hogan, a long time dedicated and pre-eminent Nikon expert & tester, comment on this and theorise that it affects image quality then that tends to sway my opinion.
Quote :
This article is based upon years of experience with Nikon's VR system, very close analysis of testing results, talks with many other professionals, and even information from Nikon insiders
http://www.bythom.com/nikon-vr.htm
The issue isn't with the sync speeds but with the VR sample rates, a constant 1,000hz. This is a quote from Nikon :
The detection of the low frequency band in camera shaking has been greatly expanded, so the VR effect has become available even if the shutter speed is quite slow.
Your comment on keeping the AF point stable is certainly valid and also it should be mentioned that the VR keeps the image stable in the VF too.
Of course you are absolutely right that it is not known if Nikon's current implementation of VR overcomes the issue of potential interference over 1/500 but still we can not disregard the weight of evidence based on just one's own (possibly flawed) testing.
It's interesting that Nikon themselves do not help in this regard, and we can only wonder why (if there is no effect then why not state that VR can be left on except when on a tripod ?), but only state (in relation to slow SS with no comment on upper limits) :
The improvement in VR II performance has been made possible by the introduction of improved movement sensors, enabling better detection of camera and lens movement. The new sensor and circuitry are able to provide a more accurate compensation of the movement that occur at slower shutter speeds, resulting in sharper images.
Nikon also state (and in this regard note the 1/1000 figure and add on the time to complete the cycle :
These sensors detect camera movement as angular velocity every 1/1000 second. Angular velocity data is sent to a microcomputer built right into lens, which then calculates the amount of compensation needed. After this data is transmitted to the VR unit, the adjustments are made instantaneously ...
Probably it's best to go with one's own experience/opinion unless it's conclusively proven one way or the other. If you are getting acceptable results leaving it on then there is no need to change. However, I'll be keeping mine switched off over 1/500