At the time of writing, there are 108 US patent applications published in the name of Facebook that mention "social network[ing, etc.]" in the title or summary. The software code is not required, only algorithms or other information explaining how the software works. This means that the novice has some chance of understanding the point behind it.
Some may sound a bit spooky, or intrusive. Here are a few. Some have already been published as B, granted patents, in which case I link to that B rather than the A document. Grant does not necessarily mean that the invention has been incorporated into the way Facebook works.
Promoting participation of low-activity users in social networking system
Methods and systems for tracking of user interactions with content in social networks
Crowdsourced advertisements sponsored by advertisers in a social networking environment
Providing relevant notifications based on common interests between friends in a social networking system
Suggesting connections to a user based on an expected value of the suggestion to the social networking system
Inferring user profile attributes from social information (as illustrated below)
Predicting user responses to invitations in a social networking system based on keywords in user profiles
Leveraging information in a social network for inferential targeting of advertisements (as illustrated below)
I haven't used Facebook since, when trying to set up an account in order to see pictures that were only visible to account holders, it immediately published my date of birth on the Web even though I hadn't specifically authorised that to happen. I'm not keen to encourage identity theft, and also felt it was very intrusive. I closed the account right away. It is, of course, the kind of data they use to infer information about people to set up possible connections, to target advertisements and so on. Knowing your income would be useful, for example...
What about Inferring household income for users of a social networking system, anyone ?