AdWords Category Targeting / Behavioural Targeting
This is something I see a lot these days…
I downloaded a Chemical Brothers album from Amazon and 15 minutes later I saw this ad on one of my own sites (photos-for-you.com):-
At the very least, this type of thing should allow you to make more money if you have a web site with AdSense on it!
If you are lucky enough to be in a niche that has a well targeted category in AdWords, then this should make the Google Display Network work better for you than just using contextual targeting…