Mark when I sold my 40D I based it on the last image number I shot and just said it was approximate as I had never reset it, not sure if the images increment if you shoot without a card though but never did that very often. For example my last shot on my 7D had the filename of IMG_8332 so I would say that was approximatly 8332 shutter actuations.
Good luck with the new camera, as I said in the AI servo thread I know you will put it to excellent use
