The Facebook iOS SDK 3.0 Beta says "These new features work with iOS 4.0 and later." Does that mean that it won't work on iOS 3.x? Does that mean that if I have an app that supports iOS 3.x, I cannot use Facebook iOS SDK 3.0?
Correct. Facebook iOS SDK 3.0 will not work with iOS 3.x. We felt that the productivity enhancements (e.g. blocks) in iOS 4.x were simply too useful. The SDK is open source, and we plan to maintain the history, which includes the existing code that does work with 3.x. In this way there is still an option for applications that need to continue to support older versions of iOS.