Facebook wants developers to create subsets of the Open Graph around interests and things. Yelp might create one around restaurants, Pandora might create one around music, Netflix around movies. Add some “like” buttons and anytime someone likes a restaurant, song, or movie anywhere on the Web with a Facebook like button, that information will flow back into the Open Graph. So that Yelp will know what restaurants you and your friends have liked elsewhere and take that into consideration when giving you recommendations, or Pandora with music, and so on. (Yelp and Pandora are real examples, Netflix isn’t).
Read more: Zuckerberg: “We Are Building A Web Where The Default Is Social”
It's already live on some pretty popular sites. Feel free to check out any movie on IMDB for example, or any story on CNN as another.
On one hand I find the implications of this to be disturbing since Facebook is a private company and as of this time to the best of my understanding the API's to extract this data are private. On the other hand the moment they bake this into a behavioral advertising system shit's going to get real.
I'm of the belief that it also works both ways, as in those sites that hook into their system in this manner can immediately gain access to a persons interests in order to market to them more effectively.
Which begs the question, why aren't the same people that hate on behavioral advertising freaking out about Facebook privately gathering peoples interests across the web?