It is important to remember that it is still up to publishers whether to participate in Google’s behavioral targeting network. (It’s opt-in for publishers and advertisers, opt-out for consumers. Hmmm.)
The concern is that Google’s contextual relevancy may dwindle down, in exchange for behavioral relevancy. Contextual relevancy is what Google takes pride in, they love to say they have ads that match the exact content of the page. If you are reading about Sony video cameras, Google will show you AdSense ads for Sony video cameras. But possibly now, if you are a sports enthusiast (Google knows this because you visit sports sites) and you are reading an article about video cameras (because you want to buy one for the next game), you may see sports ads and not video camera ads.