Google is also preparing to disrupt the advertising business itself, by replacing creative salesmanship with cold number-crunching. Its premise so far is that advertising is most effective when seen only by people who are interested in what’s for sale, based on what they are searching for or reading about on the Web. Because Google’s ad-buying clients pay for ads only when users click on them, they can precisely measure their effectiveness – and are willing to pay more for ads that really sell their products.

— From an article in the NY Times by Saul Hansell