There was a time when Apple was interested in building its own social network.
And when it did, the company was busy patenting its ideas for what would be called "Ping". One of those patents is the "user to user recommender", which is a process that is about as trivial as it sounds, but unique enough that the USPTO has granted Apple a patent for "invention".
Friend recommendation is the most basic requirement for a network that intends to help its users to extend their social network. Apple's idea closely relates to the ways how, for example, LinkedIn recommends new out-of-network contacts. In Apple's version, it just happens in relation to music: First, user profiles are being compared, including media item sets and music/video playcounts. Based on that information and the grade of similarity, the system would then assume that matching media item sets are reason enough to let you know that you may want to connect with another social network user.
Common sense would raise the question whether a patent was really necessary for this rather basic idea and even the two listed inventors could have had, in a reasonable world, some thoughts that what they have invented may already exist.
In the end, they quoted and referred 260 other patents with some ideas relating to this specific patent. The earliest patent filed in 1989 and granted in 1991 to a company called Neonics under the title "System and method for recommending items", which does not differ significantly from Apple's idea in 2011.