I bought my D600 in August and really haven't had much of a dust problem, at least nothing that couldn't be blown off with my Rocket blower. However, I did have two persistent spots in the upper left of the frame.
I just purchased a LensPen SensorKlear II and used it on the spot. It took all of 3 seconds. I then gave the sensor a cleaning with the rocket blower and took the next picture....spots were gone. It was the best 10 bucks I've spent in a while.