<<I have mixed feelings about my 80-400. At times I have gotten some pretty good shots with it. (I use a D300) and at times I've been tempted to throw it out the window of my truck.>>
Mine was ok with my D300 and D90 image wise, although it chuntered and chattered while it made up it's mind whether it would focus or not
With my D7000, for reasons that elude both me and other posters here, it still had all the focusing issues, but the images were more often soft than sharp!
Enter Sigma and all the issues were behind me as my 50-500mm OS behaves exactly as my Nikon AF-S lenses do, faultlessly. I really cannot understand why Nikon drag their feet with the upgrade of a 80-400mm, especially as Canon have, by hearsay, an excellent EF 100-400mm f4.5-5.6L IS USM and it's about the same price as the Nikon 80-400mm and that Canon lens is 8 years old!