They will acknowledge and fix instances of it when they are presented with the camera, but they will not acknowledge it as a systemic problem - regardless of whether it's been corrected or not. It may or may not be evident in every one, but as an owner of both a D7000 (where I saw it, but not nearly as quickly) and a D600 (where it appeared with no lens change after 100 actuations) I have to believe that it is, in fact, a manufacturing "problem" regardless of its current state of correctedness. Alas, formally acknowledging it means recalling all product on shelves and the potential to service every working D600 out there, even if the owner has never had an issue. Easier to handle it this way, let the "internet rumors" persist and wait for bodies to show up under warranty.
I'm disappointed with having to deal with the problem, but as long as I've got a fresh battery and an air bulb available I can keep it at bay. I shoot a dust check image before I head out, clean if necessary (air blow - I've only wet cleaned once) and check again after I get back, if only to try and determine if I have an issue. I was shooting a non-stop stream of snow geese flying overhead on Saturday and about 30 shots in from a clean sensor that morning - BOOM - a big spot appeared near the center of the bottom edge. There were two factors that likely aided this. 1) I was shooting straight up, so gravity helps. 2) I had the camera in CH mode. The latter, with it's rapid and many mirror flings, seems to bring about this problem much more quickly than when using single frame mode, acting like a fan inside the body (I tend to keep the camera in Quiet mode as it also seems to aid in reducing movement - a lesson learned with the D7000's aggressive mirror).
And while I tell these stories I will say that I have no regrets purchasing the camera. I will likely send it in for a once over after I log another thousand or so clicks on it, particularly if I don't see the problem abating. I wouldn't blame others for wanting to avoid the issue, particularly if they are not inclined to do pre-shooting prep every time they go out, or are less inclined to stick their noses inside and prefer to wait. My Dad instilled a bit of a rule in me long ago that says if you want to use a particular tool then you better be willing to know how to maintain it. That means changing your own oil and tires on a car, strings and electronics on my guitars, and at least knowing how to check my cameras and lenses for dust and getting rid of it when necessary. YMMV, but if I had to send stuff in every time it needed tweaking I'd be spending a lot of time at the post office.