I don't have my M3 yet but for my 325....
In between my personal weekend hand car washes I take my car right down the street to a laser touch-less carwash ($6). It is one of those that you park in and the machines moves around your car. No rails, no brushes and no guys hand drying your car with a sandpaper terry cloth towel.
2008 M3 Space Gray, Black, Syc Ant Wood Trim, DCT
2001 325ci Steel Gray - Sold