An anonymous reader writes: Facebook has recently introduced a new feature called 'Instant Personalization'. This will enable certain sites to give you a personalized experience.
From the article "Partners adhere to Facebook's guidelines and may only use your public information to serve you a personalized experience." Partners listed include Bing, TripAdvisor, Rotten Tomatoes, and at least 5 other sites.
I have read it is enabled by default, but I cannot verify as it has not yet been rolled out to me.
There is also an option to disable this if your profile has been affected by this. "Privacy Settings -> Apps and Websites -> Instant Personalization" to find the option on your profile.