David Rosenblatt kicked off the ISOC-IL conference describing plans for a Google Ad Exchange that would look like a stock exchange.
Why are people still spending most ads on top sites like Yahoo, when these sites have proportionally small audience? Because it's hard to figure out how to sell ads to millions of smaller sites; it's easy to just call Yahoo and buy an ad.
Google sees in the future that 95% of ads will be sold through an ad exchange (ala stock exchange). People will buy ad space in large pools and sell them to advertisers.
It's easy to use an ad exchange rather than try to find all the relevant sites that meet your ad needs. Google is aiming to build a big and liquid ad exchange. They'll still promote doubleclick for 5% of direct sales. And they will create a Google network to function as an independent ad brokers for Google's ad exchange.
For previous coverage on this, see paid content (David gave the same speech last week). (also see)