This has been a known issue for a lot of people. I was hoping this update would have resolved it. If you use iMessage, it is best to keep checking to ensure the message did actually send - sometimes it returns an error or the progress bar just hangs when sending.
My problem seems to have resolved itself by last night. No disconnects from imessage since yesterday afternoon when I had my activation problems. Perhaps the issue yesterday was related to the rollout of the update and increased pressure on the servers. I just find myself checking frequently to see if it has disconnected.