Just a reminder to the US readers tempted to deal with NikonUSA's perpetual inventory problems by buying an import: if you buy a gray market product in the US, NikonUSA will not repair it under any circumstances or at any price. Things are a bit different in some other parts of the world. In Europe, for example, gray products have a different status these days, so you can usually get them repaired by Nikon in Europe.
I generally recommend that people in the US avoid gray sources for several types of products: AF-S or VR lenses, and current DSLR bodies, especially for items over US$1000 in price. That's because NikonUSA also restricts parts, tools, and training on a lot of the more recent, complex, and expensive items. Thus, while there are a few places that will repair gray market Nikon equipment in the US, their ability to do repairs on some products is somewhat limited. I have little or no problem suggesting gray for simple items and accessories: remotes, less expensive older AF and MF lenses, and maybe even teleconverters. But as the expense and complexity of an item ratchets up, your aversion to buying it as a gray import should, too.
Most reputable places that also offer gray market versions of products (B&H lists these as "Import", for example) provide their own warranty with them. But even this can be tricky. For items that are in low supply, like a 500mm f/4 VR, one of B&H's options for dealing with any needed "warranty repair" is to simply replace the item, but the lack of supply may mean that doesn't happen as quickly as you might want it to. And, of course, once the warranty expires, obtaining parts to repair a complex lens can get tricky. Given the prices on some of these items, it may actually be simpler to just get on a plane to Japan or Canada and buy the exotic item there and bring it home. That doesn't qualify as "gray." As long as you have the receipt that shows you picked it up in the country it was imported to, NikonUSA will honor the warranty and repair the item. Mail ordering from another country and having it shipped to your US address, however, doesn't count. You have to take delivery in the country selling the item. Of course, US Customs will want to charge you for the privilege of buying out of country, too.
I've written about this before, but the current Nikon policies (worldwide, not just NikonUSA) show a strong basic contempt for customers. NikonUSA's official statement as to why they don't repair gray market products includes a large section that tries to imply that they do what they do because the products have to meet certain safety regulations and certificates. Yet, the products are all made in the same plant, to the same standards, and a Nikon product bound for the US market is now no different than one bound for any other market other than perhaps the manuals and accompanying documentation (and with many lenses, not even that, as Nikon uses multi-language manuals for most lenses now). In short, their statement is pure hogwash.
NikonUSA's justification is essentially that they don't know what's in the box or where the box has been. But that's true for the official products you buy, too. Once a product leaves NikonUSA's warehouse, they have no control over it. Nikon does not even seal most product boxes, so even an authorized NikonUSA dealer can do all the things they accuse gray market importers of doing.
Let's talk about the real issue here: money. Amongst other monetary benefits to Nikon, Nikon's corporate policies effectively reduce their warranty repair costs, mainly because they make it near impossible for some people to get warranty repairs. (An example of Nikon's disingenuousness: "refer to the warranty cards included with the product" to obtain service on gray market products. Only problem? Cameras don't come with warranty cards, and they are often pulled out of gray market products. Nice Catch-22, Nikon!)
Nikon's corporate policy is in direct contradiction of their own written Corporate Social Responsibility Charter. When products get discarded because they can't be repaired, how exactly does that promote "protection of the natural environment," for instance? Do I even have to mention the "Respect for human beings" statement? (Yes, I know that statement is mostly directed at human rights issues, but still, how are Nikon's policies really implementing "all persons receive fair treatment"? Note that Europeans get different treatment than Americans at the moment, but only because European law forces Nikon's hand. Apparently "fair treatment" means "what we can get away with under the law.")
Unfortunately, we Nikon users don't have any say in the matter other than to perhaps switch to Canon, which now appears to unofficially repair gray products in the US (I can't find any official acknowledgment of this, though I know of many cases where they have done so).
So, while it's tempting to buy gray for some of those perpetually out-of-stock products, please do more research and think about the possible consequences before doing so.