MannyP: If you are still looking for a solution to the white spots, you might consider Griot's Garage Spray-On Wax, their Dried-On Wax Remover, or 3M Rubbing Compound.

It may seem counter intuitive but Spray-On Wax works very well to remove that last little bit of hand or machine applied wax as you buff it off. Griot's also has a product called Dried-On Wax Remover, which I cannot vouch for since I've never needed to use it.

When I owned a metallic black car, 3M Rubbing Compound proved to work great on the occasional water spot and bird dropping.

On another note; my two cents on using Clay, enhancements to what others have said in this thread.
1. A mild Clay is best used to help bring back a smooth paint surface when there are noticeable particulates to the touch. You can use your fingers for this test - you can go to the back of the hand test after you've clayed, polished, and waxed the car.
2. Use plenty of quick detailer as a lubricant when claying the car. Soap & water may break down the clay and therefore do not make for an ideal combination with clay.

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'07 CS Speed Yellow