I use ONR in the winter (Indiana) on my monaco blue e92, and my wife's black jeep. I actually just did them a couple days ago. My personal belief that any time you touch the paint, you are going to get scratches to some degree. With that said, this doesn't add any more than a normal wash would. Just be careful, pre-treat with a ONR/water mix in a spray bottle, clean you mitt often, and get a couple good waffle weave towels. Plus, I would rather get some minor imperfections than splatter my car with the harsh chemicals that any of the automatic washes use. If the cars are really dirty (salt, etc..), I will take it to one of the DIY bays and spray it off really good before bringing it home to use the ONR. This also makes cleaning the wheels easier. I just bring the sonax and a wheel brush with me to the bay. The pressure washer makes quick work of the brake dust.
Current: 2011 335i e90 m sport
2009-2013: 2008 328xi E92