How does the leather skin on "Find My Friends" trick people into assuming familiarity? It's an application without a physical analog, other than shouting your friends' names really loudly or wearing a weird hat or bright shirt.
I think someone with a high position in Apple's iOS app software department just really likes that leather look, and people are reading way too much into this. There are cases where the skeuomorphism is appropriate, such as the striped yellow notepad or the wooden bookshelf in iBooks, but Apple has clearly extended the use of these themes beyond where they make any kind of logical sense, making them simple arbitrary aesthetic choices.
To me, it just looks weird, with interface elements such as buttons and text fields sculpted in leather. I cannot see how it would make me feel familiarity.
It would be interesting to see an A/B test of the leather UI and a standard iOS UI — something that looks exactly like Google Maps with Latitude on top of it, for instance.
I'd be willing to bet that the leather UI is better received by users. The app is divulging a core aspect of privacy but it certainly manages to look friendly doing it.
What you're referring to is the Contacts app (which happens to have a clean, standard-themed interface on the iPhone, though I believe it does have a leather-themed interface on the iPad). The "Find My Friends" app is a new buddy geolocation app from Apple released (in the App Store) alongside iOS 5; it's similar to Google Latitude.
I think someone with a high position in Apple's iOS app software department just really likes that leather look, and people are reading way too much into this. There are cases where the skeuomorphism is appropriate, such as the striped yellow notepad or the wooden bookshelf in iBooks, but Apple has clearly extended the use of these themes beyond where they make any kind of logical sense, making them simple arbitrary aesthetic choices.