The Social Framework is designed for simple, site-neutral data manipulation. Examples might include getting the user's 'activity feed' (as described by the docs) or posting a new status or photo. It currently works with Twitter, Facebook and Weibo however, other than lack of features, the current main disadvantage is that it is limited to iOS 6, which won't be as much of a problem in the future.
On the other hand Facebook does have an iOS SDK that makes it reasonably easy to integrate Facebook into your app, and it is much more powerful than the Social Framework. Another benefit is that support goes back to iOS 4.3.
I'd recommend using the Facebook iOS SDK over writing your own custom one and using OAuth because Facebook has already done the work for you.