Unsolicited product review: Meguiars Clay Bar

If you think "clay bar" sounds like a particularly repellent diet candy, I don't blame you.  It's actually for taking paint smears off your car, and it really works.  I actually posted about it once before, but this time I remembered to take before and after photos.
A few weeks ago my wife lightly scraped a concrete pillar in a parking garage while maneuvering to a newly opened ticket window.  The result was this nasty arc of gray on her deep metallic blue Miata.
yeccch
It looks screwed, right?  When you see that on your car your heart sinks, you just figure it'll be like that forever unless you pay someone with permanently blackened fingernails a grand to bolt on some new body panels.  But sometimes it's not so bad:
blue Miata here
Basically you buy this kit, and inside it there are "gray bars" (here actually white) in plastic bags.  You open one and knead it until it's kind of soft.  Then you flatten it out a bit, spray that squirt bottle onto the car, and rub the bar on it.  Rub it and rub it and rub it.  It took me a half hour or an hour of spraying and rubbing to do this, meanwhile stretching and folding the bar to get a clean surface.  There's other stuff in the kit too, like a soft cloth and some wax, but the clay and spray are the main things.

You do have to be careful not to get sand or hard grit in your bar, because if that grit happens to be at the surface of your clay while you're rubbing, it will scratch the daylights out of your clearcoat.  It's not too difficult.  Just wipe off the car with a paper towel before you start, and don't lay the damn clay down on the ground while you're working.  Put it in the little plastic box they gave you.  Easy!