The search partner network does not deliver value in one sector but in another it is the main source of revenue! I have come to the conclusion it depends on the busines.
Something with a high ticket price is often well researched by a consumer so their not going to come across an advert on about.com and almost casually browse to a ite and buy goods worth thousands of pounds. If something is a few pounds then a casual conversion is more likely.
This is not the full story though you also have to factor in the likely demogrpahic that is going to be interested in the product that you are selling. So an advert for a car is going to have a bigger demograhic then a motorbike.
Even that is not the full story how often does that demographic buy is the final peice of the jigsaw. For example I think about buying a new car every few monthes I think about buying a new dining table once every twenty years!
This is not to say that I'm still begging Google for more control of their Search Partner Network. A click from about.com is not worth the same as a click from AOL search.