Here's what the Clay process does, and why you should wash over it after you're done:
Claying a car removes micro-particles imbedded in the paint. If you really want to see what a clay bar is doing, just run your fingers over the paint before, and after the clay work. You'll notice the feeling goes from semi-smooth to silky, glassy smooth very quickly. This is the effect you are after. In fact, your fingers are far better at detecting surface flaws then your eyes could ever hope to be. So, that is your measuring stick...the feel of the finish.
And to who said "Wax is Wax..":
I've used Zymol, Meguires' - 3 step wax, one step wax and those crappy NXT, and Gold Class waxes, Mothers' - one step wax, and 3 step wax, countless variations on Turtle Crap Wax, Blue Coral junk (some ruined my finish!), I've tried several spray aerosol waxes used in NASCAR, I've used tons of cans of Honda Polish (an excellent Motorcycle polish/cleaner), the coveted Body-shop special 3M cleaner/polish/wax bottles, etc.
I've probably spent thousands on all these waxes and their new versions of what they were peddling. But, I learned an important lesson while making these mistakes...Wax is DEAD. Zaino is a Polish with enough strength and durability to be used in place of wax. Long live Zaino. 'Nuff said.
06 VFR, one coat of Z-2 with ZFX additive, about 1 month after treatment (didn't even clay it)
1997 Trans-Am, Pic taken in 2000 I believe, 7 year old black car. Clay/2 coats of Z-5, 2 Coats of Z-2. This pic taken about 6 months after its treatment.