[Also not the OP] One of the ways you can see this in action is with re-targeting. If you visit somewhere like SEOMOZ or www.shoesofprey.com (with cookies enabled) you will start seeing advertisements for them pop up everywhere. It feels strange (especially since I am a long way from teh target market for something like Shoes of Prey -- checking them out as an interesting Australian startup does not mean that I want to buy a custom-built pair of high heels)