Dilbert asks the key question. This is really the question Clay is asking, but the other way round - how do you know that the ad spend in FMCG or CPG or whatever you call them is actually achieving incremental sales?
What quantification techniques are used, and could one try the same techniques with Gonzo campaigns?

This reminded me of Ruth Shalit's articles in Salon a couple of years ago, such as this one about the superego of the Pillsbury doughboy. Lots more here