He's got a slide up right now measuring the impact of search. Says direct effects only account for 16% and indirect online effects another 21%. That means offline effects of search account for 63% of how it impacts buying. Basically, what he's been getting at is the need for ROI in everything but it's really a hard thing to quantify.
However, he's optimistic retailers are going to continue to shift dollars online. Here's a study they did on impact of online marketing to offline sales:
119% search & display
82% search only
Makes me feel good about being an interactive agency.