Nick,
The clay cleans things ON the paint, the scrub cleans things IN the paint. On=tar, overspray, birdcrap, bug residue. In=swirls, oxidation, etc. I have seen the claybar remove some oxidation but it excells at removing stuff that is stubbornly stuck to paint. Really gives the finish a smooth feel to the touch. BTW the Meguiar's clay is too soft. Both on a very virgin E430 (very light cleaning load) to removing paint from a "door ding" off my ex's 300E. (heavier cleaning duties) The Meguiar's clay will rub off no matter how much lube you spray on the surface. Perhaps I got a bad bar, but it just doesn't work anything lika as well as the rest of their product line. I have had very good luck with the "Clay Magic" bar. When I really dress up the finish or are working on a stubborn problem, I will use BOTH Meguiar's polish and the Clay Magic on the same area. (in separate steps of course) Only down side is that you have to discard the clay bar if you ever drop it even once. Hope this helps.

Lee