I'm glad this thread was revived, I wanted to add a couple of things:
1. I know it's been pointed out, but it hasn't been emphasized enough for me - the dust on your dirty car combined with a high-pressure sprayer (even a normal hose with a good nozzle) become 'sandwater' (like sand paper). It will scratch your paint. A fine mist spray to completely soak the car left for a couple of minutes is a perfect start, to be followed by soapy water and a soft mitt or scrubber is perfect.
2. For those who don't want to take the time to tape all the open seams (like where the door meets the side panel), or who have a car that someone in the past left a wax buildup in those seams, I found a tool that makes removal quick and easy:
First, get one of these:
It is a surfboard wax comb, most designs will work, but the one pictured here seems to work best, it's called Wahoos wax comb, available from
www.9star.com for $1.99, or most surf shops for around the same. It is made out of ABS or similar plastic, a fairly soft compound, which will not scratch paint.
Then, starting from the bottom left corner as pictured, cut the comb in half diagonally ending the cut at the upper right corner. Be sure to start in the curved, half-moon shaped section at the left, not in the teeth on the bottom. All the teeth should remain together. A hack saw will go through the thing like butter, and if you put a little oil on the blade first, you won't clog the teeth.
Now the corner where you started should have a couple of points of different sizes and angles. I have yet to come across the body panel I couldn't get one of those corners tucked into. You just run it back and forth a bit in the groove, and all the wax will flake right off. Once you get used to it, you can do a whole car in a couple of minutes. The leftover piece makes a great soft scraper, good for getting bird turds and tree sap off the car without scratching the paint.