[joshuamorton]

Ok but is anyone doing that? Even if technically possible is that a violation of the ToS? (I don't know the answer to either of these questions, but I expect that the answer leans towards "no" for both).

>If I target my ads to left-handed Hungarian mimes, and someone clicks on that ad and comes to my site, what do I know about that person?

Nothing, unless they register there, and if your goal is to convert left-handed Hungarian mimes, then you probably know about your target audience already. You've learned something about a tracking cookie. That's only valuable if you can continue to track the user.