I don't think this is iOS 6 specific, but for a while now, I get notifications for Facebook and Foursquare, but they do not make a sound or vibrate my phone (even though I have both set to ON). After doing a search, I read that many others are having this problem with Facebook as well. However, the newly updated Facebook Messenger seems to be working ok (it will make a sound), but I don't know where to pick which sound it uses?