Well targeted advertising is when you're looking for a car, and you get presented with information about cars.<p><i>Perfectly</i> targeted advertising is when you're looking for a car, and you get presented with information about a car that you buy, but that you would have bought if you spent time doing the research yourself.<p>This is my <i>definition</i> of theoretically perfectly targeted advertising. This is what <i>I think</i> Google is trying to achieve.