I upgraded my iPhone 4 to iOS 6 and don't see the ability to tweet or update Facebook statuses from Notification Center. I am signed into both through Settings. Is this only for the 4S and above? 
Edit: I found it...apparently I have to have the "Share Widget" in Notification Center. In case anyone else is scratching their heads.
Edit: I found it...apparently I have to have the "Share Widget" in Notification Center. In case anyone else is scratching their heads.