I would argue that Behavioral Targeting is nothing new and any media planner worth their calculator has been incorporating behavioral targeting into their plans for the last 10 years. The most recent definition I've seen for Behavioral Targeting is the concept that a users' actions indicate a predisposition or acceptance of a specific type of advertising; that they would be more receptive to particular messages. There used to be profiling engines that helped drive Behavioral Targeting and many of these are in vogue once again, but at the end of the day Behavioral Targeting is basic advertising. Understanding the mindset of your potential customer and developing a recommendation to speak to them directly while limiting the amount of wasted exposures is Behavioral Targeting.
Behavioral Targeting basics are executed via contextual relevancy and a well-thought creative brief. Contextual relevancy and examination of log files will typically give a media planner an idea of where your visitors are coming from and what type of triggers are bringing them to your site. Search advertising is the truest form of Behavioral Targeting as it provides almost 100% prequalification for the predisposition of the consumer. Search used to be via graphical placements and now text placements have taken over, but the concept is still the same. Beyond contextual relevancy you move into profiling where you model advertising exposure based on similar paths and actions for other people that visit a site or network. If audience member X fits into a profile, then they may be exposed to advertising that other members of that profile were receptive to viewing.
A well-thought creative brief is also extremely important. I would contend that every media planner should write at least 4 creative briefs every year (once per quarter). A creative brief is an examination of the mindset of the target audience and can be extremely useful in developing a media recommendation. If you've never written a creative brief than it's possible you have not paid the deepest level of attention to the identification of your audience. You need to be capable of doing this in order to truly understand the mindset and behavioral tendencies of your target audience. A well-written creative brief provides insight that is otherwise overlooked and goes far beyond log-files, Google searches and Media Metrix or @Plan runs.
What's funny about the buzz surrounding behavioral targeting is that I really can't find anything new in it (of course, I think that the buzz surrounding search is funny as well, since my first online campaigns all centered around search). Behavioral Targeting is advertising 101. Open any textbook and you will find chapters dedicated to understanding the behavior of your audience. There may be a new spin on it, but its not necessarily teaching an old dog a new trick. It's the same old trick that we used to use, but the reward is more immediate and trackable. Maybe that's the rub; that we can now prove the immediate effect of Behavioral Targeting with our new toys and tracking tools?