I had the same issue, I was on a holiday in GOA, India clicked some amazing pics but came home and saw lot of dust sensor issues, believe it or not i found more then 100 dust spots on the top right and left corner of the frame, it was so shocking. when i sent to the service center they denied its sensor dust, they told me that it happened due to frequent lens change. The truth is i had only my kit lens 24-85 lens mounted on my camera all the time.
I am so fed up with my camera now, it is the 4th time I am sending my camera for servicing, 3 times for the sensor dust, which got partially solved after that when i got my camera i see a black spot in the viewfinder. now again 4th time i had to send it again. I think the service center people are very careless and lazy buggers, they don't even double check to make sure everything is ok. Now i have finally decided to sell this to some one. I really do not have any patience or interest in this camera any more. I was supposed to buy D700, but fell in the ditch bcoz of flashy adds and bull shit recommendations written by some stupid money making review writers. I think i will be loosing at least 1000 dollars as the price of this camera has come down. I purchased this camera for $ 2400. What a waste. I sincerely request newcomers not to buy this camera. Instead go for a Nikon D800 or D3s or any lower end camera.