I recently did something very stupid and attempted to clean the sensor of my 350D with canned air. There was visible marks on some pictures from dust on the sensor so it needed doing. The canned air I used specifically states for photographic use and was bought from a camera shop. I tested the canned air on the camera body and on a window and didn't see any solvent residue. So I sprayed it into the body, a good couple of inches from the sensor surface. Disaster! Residue all over the sensor, must be something to do with the sensor surface.
DON'T USE CANNED AIR TO CLEAN YOUR DSLR SENSOR!!!!
On the plus side, I actually contacted Canon and sent it through their service centre as I didn't want to risk destroying the CCD by cleaning it myself. The service was excellent, not only have they cleaned the sensor up, but they've cleaned up the whole camera body. Looks like new. They quoted me before doing the work and didn't charge me until it was finished - they actually phoned me.