To keep your paint looking good over the years it is important that you do not drag all the dirt on your wash mitt and in your bucket over the paint.
One way to help prevent this is by using some real sudsy car shampoo and two buckets. one to rinse in and one with shampoo in it.
Recently I have seen a foam gun in use and the amount of suds this thing creates is incredible. The suds create a slick barrier between your wash mitt and the paint and it seems to just float the dirt right off your car. using just about any shampoo you can foam your car up real good.
Here is a picture of one in action
http://www.tc.umn.edu/~chri0975/foam2_small.jpg
I borrowed that pic from autobahn at Autopia.
You can buy them at Danase
http://www.danase.com/gifofogun.html I have seen a few other places that sell them but Danase is real good in the customer service part plus they give discounts and coupon codes. Use fathersday for 15% till fathersday.. After that you are on your own.
I hope this helps someone.