Or simply put ads only in the right-hand column that is now entirely populated by ads. "Do you want the results our software comes up with? Then read left. Or do you want the results people pay us to show you? Then read right." This would be an honest business model, and if advertisers had to provide more value to searchers than Google's algorithm with their keyword bids, they might actually do something smart and useful.
Google has more options than just the size of the box: for one thing they could make the box surround the ad (that is a common UX design to show related elements) and put the word "ad" around the entire border or the box, like police tape. That would make it a lot clearer that it was an ad.
