Don't use Dawn as a regular cleaner. It's interesting that you should ask because I used Zaino Bros. products for the first time this past weekend and the first step described in the instructions was to use Dawn to clean the surface and REMOVE THE WAX. They mention "Dawn" by name. Although my car is relatively new (2002 E46 M3 Cab.) it doesn't matter. According to Zaino Bros., even new cars have contaminents in the paint.
By the way, Zaino Bros. products? Whew! I AM IMPRESSED. Fabulous finish--like a showcar. I'll post some pics later.