Here are the results of my first attempt at cleaning the sensor on my 20D after 18 months of ownership. I am a frequent lens changer. To clean I used Eclipse and their sensor swabs (type 2 for the 20D). The cost at Thompson Photo here in Knoxville was $62 for one bottle of Eclipse and 12 sensor swabs.

For the image called after 1st clean I went from left to right, fliped the swab over and then from right to left. And repeated, a total of four strokes. Before I began swabbing I placed three drops on each side (tip) of the swab. The amount of pressure I used was enough to put a slight bend in the sensor swab stick.