I typically wash my cars and bikes by hand but I have certainly been through my share of washes, too. Some wand-only types that simply spray high pressure streams, others that have spinning nylon brushes such as the ones at most gas stations, and then the ones that I actually prefer--the stand-alone business that has state-of-the-art systems, from the pre-wash and soap application to the air-dry at the end.
The difference between all of these methods is wildly noticeable to me. You just can't duplicate the level of detail you get when you do it by hand.
I think you can avoid any paint damage as long as the brushes/curtains are cloth. The filters are fine enough to get the grit out and utilize the gray (grey?) water repeatedly.
The thing is--I don't always have time to hand-wash, especially with 4 vehicles in the household.
I would say I'm about 70/30 hand-to-machine right now.
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