Cold reading (Seth Godin)
The tsunami of data available online makes this easier than ever. It's not hard to buy data, not only about your demographics, but about how you spend your time on the web.
Which means that it seems as though that site or this ad is just for you. What could be better?
The important distinction is this: the content might be for you, but it's not necessarily about you. Take what you need, but ignore the rest.