Instant Personalization allows sites to personalize your experience when you visit them while logged into Facebook. When a site is using Instant Personalization, it draws from the public information on your Profile to make guesses about the type of content you'll find interesting.
For example, if your Profile includes the fact that you like reggae music, music sites like Pandora might suggest reggae artists it thinks you'll like or show you information about the reggae music your Friends listen to on the same site.
"Facebook Tips: Instant Personalization "
Reference : facebook101tipstricks.com