I just did a search on Hipmunk.com to fly one of our new folks out here to Minneapolis. Minutes later, on Facebook, I get a retargeted ad with the fare I was just looking at. This is something called dynamic retargeting, where you can show messages based on a rule– the product they just saw, how many pages on your site they visited if they are a high-value customer, or whatever. If you’re an e-commerce or have a LOT of product SKUs, then you need to use a 3rd party retargeting partner (through FBX– Facebook Exchange). If you don’t need complex logic, then use native Facebook retargeting (called WCA– Website Custom Audiences), where you can still apply url-level rules. Google has been doing this for years, so if you want the “full embrace”, you’d run with Facebook and Google retargeting together. An AdRoll or Perfect Audience can do this for you via one-stop shopping, but if you’re small biz or not super complex, you’re better off setting up retargeting directly. And they’re still at it but with a different variation.