Deep inside the Apple iOS 4.3 SDK, there is a handle called Find_My_Friends which some have interpreted as being an indication that Apple is looking to offer a location-based service that helps user to find their acquaintances.
Macrumors, which came up with it first, shows that the service may be link to MobileMe and may include an optional opt-in key.
A "Find My Friends" feature will allow MobileMe to justify its high annual $99 cost although, no one would probably get MobileMe to benefit from a social networking feature.
A location-based social networking service will pit Apple against Foursquare, Google Latitude, Facebook Places and to a certain extent Twitter.
Apple has already seeded social features in many of its services including Ping for music and GameCenter but they currently operate in an Apple controlled environment (either iTunes or iOS).
The other theory is that the "Find My Friends" could be used for Apple's iAd platform for location based services.