I've used one for almost 4 years and love it. My car sits outside most of the time, so it accumulates dust over night. I wake up, go outside and take the CCD to it, and QD it.
In the 4 years, I haven't produced any scratches from using it...nor have I had a problem with it streaking.
Although, I haven't used it when it has been dirty. Just when there is a light dusting over it.