Notice to Nikon
Putting this here because it's as much of a comment on the quality of third-party lenses as it is a condemnation of Nikon. You see all the time in these forums and elsewhere people asking for stuff and saying they will switch if their chosen brand doesn't provide what they want. Sometimes that happens but more often than not I suspect it doesn't, for a wide variety of reasons.
I think the Tamron 150-600 is a good example of this actually occurring though. It's easy to find the tremendous number of posts asking for a longer lens from Nikon, at a better price. 6 years ago the Sigma 150-500 got my money, that would have gone to any Nikon lens that was even close in serving the same purpose. Now six years later my money went again to Tamron, instead of anything Nikon could provide, and I couldn't be happier. The demand for the Tamron has been amazing. It seems to be out of stock just about everywhere, in every country. There appears to be wait lists everywhere and with the few dealers I've talked to, the lenses are just going out as fast they come in...all money that could have gone to Nikon.
I really commend those at Tamron for recognizing the demand for such a lens, taking a gamble, and coming through with a product that I think for the most part has exceeded everyone's expectations and set a new standard. Will it drive Nikon? I doubt it, they'll probably just produce another 18-55 lens or something. For me this lens took away money I would have spent on any longer Nikon, and even a possible Nikon 300mm f/4 with VR (w/ converter). Believe it or not, it even eliminated any desire I had for the 600mm f/4. They are obviously not equivalent in any way other than maximum focal length, but if I had ever been able to afford that lens, it would have been a compromise because I like to hike very far with my equipment and the weight would have been a real issue.
Anyway, with all the people who have already bought this lens, and all those who are still waiting, I sure hope Nikon sees that people will put their money where their mouth is. We weren't asking for something we didn't want and we weren't asking for something that couldn't be done. Only Tamron will be able to say whether this lens turns out to be profitable for them, but it sure has increased their brand recognition and reputation and satisfied a lot of photographers who have asked for this from Nikon for years!