I've experience this as well, though, not to the length that a photo becomes completely useless. It's still sharp, but noticeably LESS sharp..
I've noticed that while on my tripod, say, taking a shot of a sunrise or something, the camera will move slightly when the shutter clicks. I usually get sharper shots by turning VR off, but I have noticed this phenomenon as well with non-vr lenses. Weirdly, handheld I don't have issues unless obviously, my shutter speed is too slow for me to handhold effectively.
I'm not exactly sure why, even with faster shutter speeds, the camera seems to move ever so slightly. Perhaps my tripod is not stable enough to hold the camera in place? It IS a cheaper one. Perhaps it's just the way the D5100 works, being a lower end model the components might be less "solid" inside the body, leading to a bit more shake when the mirror drops? Maybe I'll try to take a video of this happening so that others can see the effects, but without a tripod for my phone, i wonder how effective that would be