It's as if the Big Brother were wearing a gray flannel suit and had three-martini lunches. One banner knows were I'm going, another -- what I'm looking for. This display unit from eBay showed up on YouTube on an unrelated search page and scrolled through half a dozen active auctions for photo gear, including one for a remote cable release for a Canon I've been looking for. The images are actual auction thumbnails. If the banner freaks you out, you can click on the AdChoice link at the bottom that takes you to an explanation: "We sometimes use information we have about you to help ensure the ads you see on eBay and elsewhere are as personalized to you as possible."
I usually find myself in the camp that defends this kind of targeting, but once, an overzealous travel company banner almost ruined a surprise trip by shouting "So, you are going to Vegas?" on a computer I was sharing with the surprisee. Caution, people, caution.