... from both my nikon d200s, tiny little spots were showing up on the images, so that's the number of photo sensors i had to clean this afternoon ... $80-125 to have the task performed "professionally," but i've learned from experience that about half the time the camera will be returned dirtier than when it was sent ... i taught myself to do the job myself using eclipse reagent grade methanol, lint-free non-abrasive laboratory wipes from the same company, and a cleaning spatula home-made from a filed down wendy's plastic knife ... $125 for a new moire/anti-aliasing filter, i learned the hard way that single piece of grit only 2/10,000 of an inch across acts on the filter surface pretty much like a skater's blade on freshly surfaced ice, so the process is absolutely one of those for which "cleanliness is next to g*dliness" ...
... this is what a squeaky clean nikon dx sensor looks like ... picture's of a white computer screen, taken with no lens on the camera ... in case you're making plans, one of the tricks is to make sure the image is grey, not white, adjusted for high-contrast ...