But secondly, invest in a Sno Brum - that thing is WONDERFUL for clearing off the car, safely. What I usually do is use the Sno Brum to push the snow off the car, then like @SabrToothSqrl said, turn on the heat and let it warm up. Usually very little left at that point. Anything that's left, sometimes I gently smack it with the Sno Brum and then it breaks apart and I can slide it off.
I really can't recommend the Sno Brum enough - one of the most important vehicle accessories I've ever bought.
Thanks for this info. Last week my M3 sat outside at a friend's house and got about 7" of snow on it. I used the typical snow-removal brush to clean the main parts of the car. Paint looks fine, but I held my breath as I did the cleaning, fearing that it might cause problems. I do have the PPF on the front and ceramic coating overall. I'll get the SnoBrum.