I am religious about doing my best to keep the D200's sensor dust free. When I'm changing lenses: prepare the replacement lens to reduce changing time; remove camera/lens from tripod; point camera/lens downward; remove lens; attcah lens; remote camera/lens. If windy or windy in a dry dusty area, stand with my back to the wind before staring the process. At the end of the day, I clean all lenses, lens caps, and the body cap.
And the sensor still gets dirty. The D200's sensor has been professionally cleaned once already; the tech showed me how to clean the sensor; and I bought the sensor cleaning kit, which I will be using for the first time.
I can easily fix the spots in Photoshop. But being the OCD poster boy, I'm becoming pretty obsessed about this.