I don't believe that dish soap will damage the car but there are many clueless owners that regularly wash their cars with dish soap and that is a bad thing unless you wax your car after every wash. It is common knowledge that if you use dish soap it will strip/remove wax and that is the only real problem. Like Pete said if you use if before a major detail job to remove all the grime and old wax then that is common but for your regular washes it is definitely a
and besides dish soap really isn't that much cheaper then a decent auto wash product since most car wash soaps are concentrate and don't take too much to was a car.
Just my .02
