That's called retargeting. Not sure if the Facebook Ads platform offers any kind of retargeting options (besides targeting based on Liking something), but many ad networks do. For instance, I spent some time looking at Photoshop on Adobe's site. Ever since, I've seen a ton of ads for Photoshop. It's a really effective tactic, since you've already prequalified the user's interest from an earlier online action.
The way it works is that the ad network puts a pixel on the photoshop page. When your browser sees that pixel you get cookied by the ad network. Then when you see an ad placement from that ad network then you'll maybe see campaigns targeted to the BT profile.
With ad network pixels it is hard to get reach. This is were companies like BlueKai fit in. They make a deal with Adobe and lots of others to put their pixel/JS on Adobe's page. Then when an ad network gets a campaign that needs to target photoshop users, they buy profiles from BlueKai.
Basically, BlueKai will piggyback the ad network's pixel on the BlueKai placement, either by injecting it via javascript or by doing a 302 redirect. This has to run for a couple weeks until the ad network has got enough reach for that profile, then they can start the re-targeting campaign.
That's how it generally works, I don't know if BlueKai actually has a relationship with Adobe.
