Just look about the significant differences of usage of sponsored links vs. image based advertising in certain industries. E.g. Sponsered Link shares goe from 2 percent (telecommunication) up to 36 percent (b2b) ...

This is just a snapshot with data from Nielsen//NetRating AdRelevance for November 2006 (US) published from the Center for Media Research (Researchbrief 19-Jan-2007)