I wash mine weekly and finish it up with a detail spray wax whether it needs it or not. It has never seen a car wash.
One time the dealer washed it when it was in for a routine maintenance, but when I saw their detail department drop a wash rag, pick it up and continue without rinsing it, I made up a sign for the dash which said DO NOT WASH and made the S/A write the same thing on the repair order.
2003 330i (wifes) sold 10/27/06 replaced with 530i (7/21/06 ED) 9/28/06 re-delivery
2001 540i (rear ended & totaled 8/17/05)
1986 535 e28 (beater, but working on restoration)