I can only say that I use AP set to f/11 most of the time,and use a rocket brush when I see dust. Now on the D80 I had to have a blow with the rocket about every month,because of the blobs in the sky (UFO,s)? But since getting the D300 in late Jan I honestly haven't seen any ufo,s.
-------------------- Got a good camera, now to get a good photographer.:~<