Google left it up to the individual sites whether or not to participate, but stipulates that to do so, publishers must provide new disclosures in their privacy policy and a link to Google's privacy policy. Estimates by Jim Brock, founder of PrivacyChoice and a former Yahoo senior vice president, suggest about 25% of AdSense sites serve targeted ads.

Using links to Google's privacy policy, Brock calculated June and October adoption levels by counting links to Google's privacy policy. Google counts 94,600 links in June and 277,000 links in October. Yahoo counts 78,000 links in June and 224,000 links in October. He comes up with 25% by splitting the difference and dividing it by the one million AdSense publishers Google disclosed in its latest earnings call.

Brock calls the pace of adoption low, given the higher revenue expectations for behavioral targeting and Yahoo's apparent success with the technology on news sites. "If three-quarters of AdSense sites are still hesitating, perhaps Google hasn't shown them the money just quite yet," he says.

"BT is somewhat of a scary acronym for some folks because they're not aware of all the issues," says Kevin McKenzie, founder and CEO of JiWire. "It's somewhat of a liability that publishers have to think about [it]. If the majority of their revenue comes from traditional AdSense campaigns without disclosing information about users, why dig into BT if there's no sign of its being more lucrative?"

Publishers read something about privacy policies being presented in Washington every week, and there's probably some degree of concern, says Bryon Evje, executive vice president of sales and business development for SpotXchange.

"Google controls so much of commerce online that many media companies are concerned about giving away more data or revenue," Evje says. "Just because Google writes the check every month that publishers can sit back and collect, it doesn't mean there's a high degree of trust."

Some believe privacy concerns have caused slow adoption rates, while others point to optimization and the sheer fact that publishers just don't understand the technology, and Google hasn't pushed it.

Len Bilello, vice president of sales at SpotXchange, doesn't think publishers have adopted behavioral targeting as quickly as many industry insiders first thought they might, because publishers don't know how to optimize the campaigns. "You need to control it, optimize it, and you're probably going to need some kind of cost per lead," he says.

Consumers also contribute to another problem. "People generally are lazy when it comes to the search experience, [so] collecting explicit feedback data, where the consumer actually tells the engine what they prefer, is something extremely hard to come by," says Dave Harry, Reliable SEO founder. "We can see this with the poor adoption of Search Wiki and Side Wiki. If people aren't expressing their interests explicitly and participating, the pool for ad targeting is diminished."

Harry believes there's a market for using behavioral data, so rest assured adoption will pick up. Privacy and laziness aside, could it be that publishers just don't get it?

"Behavioral targeting and the data that comes along with it is something a lot of folks can't get their head around," he says. "This potentially plays into the problems the service seems to have. At the end of the day, I believe it seems that users must actually supply 'interests.'"

Another serious problem is that the network must have a substantial consumer user base for the service to become effective. Along with Harry, I believe behavioral metrics will become the future, and Google just isn't pushing the service hard enough. In fact, of the more than a dozen search engine marketers he and I spoke with to create this piece, few had even heard of the program.