Oh, please, I have a very good idea of normal software development. Just because I just became "a Mac" doesn't mean I don't know how things work. This is Apple, who have always been overly-secretive about their stuff. I'm not arguing for or against this Social Networking in Address Book stuff (more below), I'm just wondering why people are categorically denying newer builds because they have sort of entitlement to Apple news.
Once again, Apple can do whatever they want. It is entirely their ecosystem. Who would they be catering to to introduce features very early in advance? They don't have OEMs to worry about, they can test and add new features whenever they want. I'm not even implying this is a last minute feature; how would you know? Many apps (including Address Book, I'm told) don't have full translations in 10A432.
And why wouldn't Social Networking support be a good idea in Address Book? Twitter and Facebook aren't just about chat. Address Book would be a good place to put them because Facebook allows all sorts of information storage like phone numbers, birthdays, etc. Address Book can act as a hub to open iChat, TweetDeck, etc.