I know that it's accepted wisdom to turn the IS off on an IS equiped lens when using a tripod, due to the potential for resonance doing more harm than the IS does good.
I only have one lens with VR (Nikon for IS) and only turn it on when I need it. So unless you actually need it, you may as well leave it switched off. Or you could try one photo with and one without and see whcih is best.
I left it on with a 70-300 @ 300mm on a monopod at the BTCC and it made a bit of a difference. I wasnt going for massive panning blur though, just catching them coming round the corners front on style