When I see spots in shots, I shoot a picture of either my computer screen set to an all white image, like a blank page in my word processor and shoot at f/16. Then I use the levels adjustment in PS6 to increase the contrast. It will show the most minute dust speck. So far I have only had to blow off a few very small items with no wet cleaning required.
The above shot was just to illustrate how the D600 performs in very low light at a fairly high ISO. The colors were great even with the mixed light of florescent, incandescent and Christmas tree colored lights.