With some lenses, especially some of the more expensive exotic lenses, you can save a fair amount of money by purchasing a "gray market" version of the lens rather than the official import. I do not recommend doing so except in a few cases (which I'll get to in a moment).
First, let's examine what happens in the US:
- Officially imported lenses end up with a five year warranty if your register them with NikonUSA; gray market lenses have no Nikon warranty and only whatever warranty the seller provides.
- Officially imported lenses will be repaired by NikonUSA out of warranty; gray market lenses will not be repaired by NikonUSA, though they may be repaired by some Nikon Authorized Service Centers.
- Officially imported lenses are worth less at resale, because savvy Nikon users understand the consequences of the above two items.
Back when lenses didn't have in-lens motors, VR components, other complex electronics, and NikonUSA sold parts to anyone, almost any competent repair shop could do most lens repairs. That tends to still be true for older lenses (AI, AI-S, and even some earlier AF lenses), though parts now tend to come from other unrepairable lenses. But for modern lenses (AF-S, VR), only an Authorized Service Center can get parts and would have the equipment necessary to do alignment, and warranty repairs would generally only be done by NikonUSA, who as I noted won't work on gray market lenses.
Thus, I don't recommend trying to save money by purchasing gray market AF-S, VR, PC-E, or other sophisticated lenses. There are still a few less "electronic" lenses in Nikon's current lens list, such as the 105mm and 135mm DC lenses, and it might be acceptable to purchase a gray version of these lenses if the price differential is big enough (remember, you're losing the five-year warranty, though).
Note that my advice here isn't the advice I wish I could give. I don't control NikonUSA's policies, I can only respond to them. Frankly, Nikon's policies for warranty worldwide suck. Nikon is trying to keep a few extra dollars in their pockets at the expense of its customers. I strongly disagree with their policies here. Unfortunately, they haven't changed in over a decade of people complaining about them, so we're left with having to deal with them as they are. That means that gray market products have substantially less value than official imports, and that's less value than the prices they fetch from dealers, in my opinion.
Buying gray is a bit like gambling. If you get a perfect sample and never drop it or never have problems with it, you win the bet. If you get a sample that needs immediate repair, you probably lose the bet, though a reputable dealer will generally handle this well by just replacing the sample (a much more graceful response than Nikons, for sure, and another reason why Nikon's policies suck). If you drop the lens or it eventually has a problem, you may or may not win the bet depending upon what the problem is and whether the lens is out of warranty or not.