Great point. I've always been puzzled about how advertisers get any ROI online. I'm a very heavy internet user on a variety of topical areas, and my lifetime value for a content site is zero. Exceptions are NY Times, my local paper and Gartner, where either my employer or I pay for the content.

I rarely click on ads. I've probably been a successful ad conversion less than a dozen times since 1996.

Print is different. Getting ads is a significant reason for having a newspaper subscription. Many magazine ads are both more useful and more effective than the ad units that you se online. I probably made a Nikon/Canon decision based on a combination of print ads.