Some Nikon cameras (I think maybe all but the D800/D800E, but am not sure about that) activate VR with a press (either partial or full) of the shutter button. The D800/D800E activates VR with a press of either the AF-ON button or the shutter button. Some shooters don't like this feature of the D800/D800E because it causes some additonal battery drain during the focusing process (while holding down the AF-ON button). I only have two Nikon DSLRs, the D200 and the D800E, and those are the only cameras with which I have actual experience. The D200 works the "old" way, triggering VR only via the press of the shutter button. Ther D800E works the "new" way, triggering VR via a press of either the shutter button or the AF-ON button. I have both cameras set up to focus only with the AF-ON button.
With cameras that work the "old" way, VR is still engaged at the time the shutter button is pressed if it is engaged on the lens. It is just not engaged during the focusing process if one initiates focus with the AF-ON button.