The below excerpt from this interview states my pov on the future of online display advertising very clearly.
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Let's talk about overall targeting. It used to be people bought media with a site-centric mentality. It was a legacy of the print planning and buying business. You looked at what sites indexed or reached your target. Today that site-centric mentality probably represents about 70% of the overall display media spending. But there really is a shift going towards this audience-centric buying methodology. Marketers and largely brand advertisers are recognizing that there are alternative ways to reach target audiences.
We believe that no matter what the overall demand for display media, there is a shift happening from site-centric buying, which is usually more expensive and the softest area of the display market. It is going from 70% to 50% very fast. A lot of that is reliable behavioral targeting, not absolutely dependent on what site you are running on.
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He calls it "site-centric mentality", I've called it "content as a proxy" but either way, the world of online display advertising is changing.