Sadly the pictures didn't turn out good of the results... But I decided to use a clay bar on my '01 Pontiac Grand Prix GTP (LOVE that supercharger!!).
I was having a problem with getting lots of tiny black "dust" particles all over parts of my car.
Basically, I'm getting most of it on the very rear of the car - from bumper up to spoiler. There is also some that gets into the rear door cracks. I've had this car for almost a year now and I've seen it since the first time I washed it. It's got to be an environmental problem.
Well, I took the plunge and got a Mother's Clay Bar kit. I was extremely impressed with the results. The black dust particles would never go away. I could wash off the new stuff, but I still had old particles that seemed to be ground in. So I put the clay bar to work and I was probably able to get rid of 98% of the particles. Then I used the wax that came with the kit to seal it all up. I highly recommend using a clay bar - it's just time consuming. I probably spent 2.5 hours total on the car today between washing, claying, and waxing. But I should be good for a while.
A picture is below. You can see in the left side of the picture that there are not any little black spots but there are still some on the right. The left side was after using the bar and the right side was before. NOTE: Pictures are AFTER just washing the car.
This picture is a before shot - you can see some of the larger particles a little better (there are lots of smaller particles not as visible in the picure that the bar got rid of too!)
This picture is an after shot - MUCH better... =)