By Jodi Xu

If you’ve recently searched for digital cameras on Google, chances are, you’re going to get something advertised on your home page or blog: a digital camera.

With the precision of a surgeon, marketers are getting increasingly sophisticated about trying to link online search habits with advertising dollars. Once fairly crude, such so-called behavioral targeting now collects data from all corners of an online user’s activities, including search keywords, Facebook fan clubs list, gender, age, and  geographic location. Marketers then use these data to predict what a person might want to buy before the purchase takes place.

“We don’t guess, we figure you out and know what you want and how much you want to pay,” said Sheldon Gilbert, 33, CEO and founder of Proclivity Systems, a behavioral data provider based in New York.

The tactics, of course, are not without controversy. When Google started to show targeted advertising using keywords in its subscribe email accounts, many Gmail users were upset to see how many relevant ads were popping up on emails. Behavioral targeting goes into more detail. It not only records the past purchase information and tracks past online activities, it also follows the list of frequently-read blogs and Web sites, and remembers the favorite products that recently showed up on your Facebook walls.

Gilbert said his clients have doubled their click rates, the number of people who click on the ads to go to the advertisers’ home page. Another New York-based data tracking provider, Datran Media, also said from its internal survey, its clients’ ads click rates doubled or tripled after feeding ads using behavioral targeting.

The silver bullet for online advertisement? “I don’t know about silver bullet,” said Lars Perners, professor in consumer psychology at University of Southern California, L.A. “But it is taking the targeting to a whole new level that makes it a potential viable online business model.”

For years, marketers have struggled with how to target the one billion Internet users that are registered on social networks. Experts have estimated that more than $20 billion is ready to be spent online. But it is hard to get relevant advertisements to relevant customers. Figuring who likes what is the most difficult part of the job. For that, marketers need a huge database that contains all the information about each online user. But so far start-ups like Proclivity and Datran, who might have the break-through technologies, have not grown big enough to build such a database.

“If I were a technology provider of behavioral targeting, I would be thinking about how to merge with big social networks like Facebook or Yahoo,” said Kenneth Wilber, professor in online marketing of University of Southern California. “It’s hard to build its own database.”

Mergers are inevitable if the model is to succeed, according to Wilber. Even then, “I think behavioral targeting will only become a successful business model in three to five years,” said Wilber. “Longer than most people would think.”