The side view mirror defrosters work very subtly anyway, so I wasn't sure there was a problem with them, but I mentioned that I didn't think they were working when I brought my car in for an oil change and they replaced the defrosters under warranty. They told me to avoid the problem in the future, I shouldn't leave the defrosters in the "on" position. This appears to be a common problem. I know numerous other VW owners (not just Beeetle owners) who have had the same thing happen.