In a shareholder letter that accompanied its quarterly report, Netflix gave some details on how they plan to make the service more social. The idea that stood out the most was using Facebook accounts to split Netflix viewing into individual profiles within the same house. So you log on to Facebook through Netflix (or maybe the other way around, I don't know) and it knows that you like action movies and someone else in your house likes sci-fi. You're served recommendations accordingly.
Facebook integration would presumably allow Netflix to help users do things like share their personal viewing history in their newsfeed and recommend videos to friends. Understanding social networks could improve Netflix's famously honed recommendation algorithm. It might also be an opportunity for Netflix to create social viewing experiences.
In a statement, Mark Zuckerberg said, "FACEBOOK CONQUER ALL! FACEBOOK SMASH!", not really.