I think there's a line that's often crossed. If there's no (or light) personalization, the ad shown will be relevant to the content it's next to, and maybe not relevant to me. If there's too much personalization, the ad shown will be relevant to me (or my browsing history), but not really relevant to the content it's next to. I would be less creeped out by personalization if the ads fit on the page; so when I view a news article about the Pope's visit, probably don't show me retargeting ads for a service provider whose API docs I was looking at yesterday; but if it's a technology site, then go ahead. Also take a lesson from Target; just because you can figure out I'm pregnant, don't make it obvious you know, put some deliberately mistargeted things in there too, so it looks more random.