Mine has a very slight lag. But the lens is only 7 months old. From comments on the forum it seems that the A/M selector ring (push the button, and turn) is prone to breakage. A few folks complained that the A/M switch was repaired by Nikon, and would then break again only months later.
Consequently, I don't play or fuss with it. I don't touch the focus ring, and I leave the switch on A (for AF) , and that is that. I understand it is a $200 repair if things go wrong.