As many early D600 customers reported, I have also started to notice some annoying sensor dust in the upper left corner of the sensor on my photos. I did as Nikon recommended in their service bulletin - run the sensor cleaner on the camera and use a brush/blower on the sensor and that seems to have done the trick. I just wanted to put that out there so folks know that this simple cleaning can do the trick. That said, my sensor dust was not nearly as bad as some of the images I have seen online from folks who have had similar issues. If it comes back, however, I will likely send mine in to Nikon for repair.