Alex at Google is explaining Google’s decision to buy DoubleClick and in doing so offers one of the best advertising primers I’ve run across. People seem to have an enormous difficulty understanding why contextually targeted search ads tend to be a lot more effective than offline advertising and this will help them. Online banner ads are probably just as crappy as offline ads. This is a key reason Google has done so well – they dominate the contextual ad market while Yahoo has struggled to deliver a similar quality product. Yahoo now has a good contextual ad product, but some think it’s too late for Yahoo to capture a big part of this market. My view is that the game has only begun.