I had a set of BMW wheels powder coated a few years ago, they dip them in something like acid to strip them, repair any scratches and chips then beadblast the wheels. The wheels are then electrically charged and coated with the powder before baked in an oven to melt the powder over the surface.
I have just had my MB wheels painted, I beleive that is how MB wheels are originally done and most manufacturers are going that way.
I think the paint looks better than powder coating, not sure which will last longer, I will let you know in a couple of years!