It appears Amazon integrating Facebook into recommendations. When activated, you'll see dedicated Amazon Facebook page within recommendations based on information in your Facebook profile. For e.g., you'll see most popular books, DVDs, and more that're listed in your Friend's Facebook profile.
You'll also see upcoming birthdays and find your Facebook friends' Amazon Wish Lists more easily. And you'll get gift suggestions for your friends based on their Facebook profiles.
Amazon says "it'll not share your Amazon account and purchase history with Facebook. And Amazon willn't contact your Facebook friends.