This is happening to me with both iMessage and SMS. If I have a message open and the person sends me a new message, it does not automatically display at the bottom of the message screen. I have to actually click the "Messages" button to go back to all messages and then go back in to see the new message. Just an annoyance but I'm wondering if anyone else is experiencing the same thing. I'm surprised...there have been more bugs in iOS 5 than I can remember for any previous release.