I have a 1998 Ram pickup that spends its entire life outside, parked near trees.  I hadn't done much with paint care for more than a couple years and one side was covered in small, hard, brown tree sap spots.  Reading the reviews on Amazon (and other websites) for clay bars and their use in cleaning up paint surfaces, I thought I'd try this Mother's kit to revitalize my paint job.  I was sceptical about its abilities to do anything other than a final "fine cleaning".  I was right.The clay bar could not remove any of the hard tree sap marks.  It does not remove scratches (and can actually apply some if you do not keep the clay lubricated.  It does make the paint seem smoother to the touch, but I cannot tell the difference between a final normally waxed and polished surface and a clayed waxed and polished surface.  The surface feel of unpolished paint Vs clayed paint does exhibit a noticeable benefit from claying, as the makers claim.  However, applying a good polish achieves the same results on a washed and clean paint surface, in my opinion.  Even on my truck, after cleaning it first, the clay stayed pretty clean and only after doing the whole vehicle paint surface did the clay feel faintly gritty and appear slightly darker in color - ready for trashing.To remove the sap, I resorted to a rag soaked in mineral spirits and plenty of elbow grease.  To eliminate any light scratches, I used T-Cut.  Then I clayed it, followed by polishing with Turtle Wax.  After a day of that, my shoulders ached bad, but the truck paintwork looks good; well, as good as an 11 year old, well-used, stone-chipped and scratched truck can.  The clearcoat has actually held up exceedingly well over the years.I haven't tried clay on our 3 year old, garaged minivan yet.  It will be interesting to see if it removes minor swirl marks.  I don't expect it to make the paint look any shinier after polishing. It looks great as it is.I did buy an extra bottle of detailing spray (I bought the kit locally at Autozone) in case one wasn't enough.  But one was enough for one clay bar / one vehicle treatment.  Since there are two clay bars in the kit, then the extra bottle will be used with the second bar.I found the claying to be easy and quite quick.  I split the bar in two, then pressed it flat into a disc about 2" in diameter.  Then I sprayed the surface and rubbed the clay back and forth over the paint in my palm.  Knead it regularly back into the 2" disc, as it gets thinner and splits.  It was actually very straightforward and no big deal.  Avoid rubber parts, like the windshield surround, as the clay picked up black "soot" from those.  Make sure you polish it dry as the spray leaves streaks if you don't remove it with the supplied towelI suggest clay bars are really for the guys and gals that want the ultimate care for their newer vehicles.  It may not be noticed by anyone else, but it's the satisfaction of a job well done that always matters to the perfectionist!  I know 'cos I am one!Sept 26 2009 UPDATE:  This evening, I tried claying half the hood of my minivan then waxing it all to see if I could tell any difference.  The clearcoat on the van is in great condition.  I washed the hood and dried it.  Then I clayed the left half (LH as seated in the van).  I did notice that even with plenty of spray lubricant there were a few faint straight line, light scratches visible in the clearcoat after I wiped the surface dry that weren't there before claying.  I could not feel any real difference in the surface smoothness from the clayed to the unclayed side. The clay appeared to have no visible dirt in it.  I then Turtle Wax'd the whole hood.  After that, the straight line scratches were gone and there was no VISUAL difference from clayed to unclayed even with the reflected overhead flourescent light from my garage as a guide.  I then applied my dry finger tips to the hood; left hand on the unclayed side and right hand on the clayed side.  Applying a light pressure and sliding back and forth, I think I detected a slight reduction in friction as the fingers change direction on the clayed side.  Even swapping hands over, the result seemed the same, ruling out differences in my finger tips!  However, the effect was so slight that it was almost imperceptible.CONCLUSION:  Claying may help with a contaminated paint surface to remove those last little imperfections and revive the paint, but with a clean and regularly-waxed paint surface, claying probably isn't worth the cost nor the effort.