Turn off sync documents and data in the iCloud settings. That's what worked for me on my iPhone 4 and iPad 2.
I think this was a trick posted by the guys who had the GM release and were having this problem with keyboard lag on the password and iMessages. Surprised this wasn't looked at before OTA release as it is really annoying to sit and have to wait a few seconds, particularly if you are going between text and numbers/symbols. Sucks that until this gets fixed, your data and documents won't be synced to iCloud just for keyboard lag.