Isn't this just the McDonald's v Subway/Burger King example? McDonald's has the research and foot traffic. Rather than do your own, watch where the successful McDonald's go and then put your restaurant across the street.

If you have a bunch of users searching for "XYZ" on a different search engine and consistently going to link A -- wouldn't that imply it was relevant? You'd do the exact same thing for searches on your own search engine. The only difference is people have opted in to allowing you to have this info _implicitly_ by going to your search engine vs giving you this permission _explicitly_ by clicking through the EULA for the toolbar.