With remarketing, Google introduced a service that lets homepage owners reach out to visitors even after they have left the website. So, a surfer who for example abandoned the order process can later, on a completely different internet site, be shown an ad that entices him to come back and complete the process.
For the average user, this will be somewhat creepy. He’s accustomed to see ads relating to the content of the page he just looks at. That’s a perfectly natural thing. But then he’s for example looking at a car-review page and sees an ad for the obscure italian town he was interested in 3 weeks ago. Will he be pleased and book his holiday there, or get creeped out? I suppose the latter, because he must assume that every step he does on the internet is watched and recorded, voiding his privacy. And that feeling will seriously hurt e-commerce sales. For the very least, it will further damage the clean image of Google, as the entity whose name is below those stalking ads.
Technically, the remarketing feature works by letting homepage owners, say a ticketing company, insert tracking code into their pages, every visitor on those pages gets served a cookie by Google. If the user later browses pages within the Google Content Network, he is recognised, and Google can serve ads that the homepage owners designed for them. The ticketing company could have some categories like musicals or football matches, and if the surfer before visited a musical category page, can then be shown musical related ads.