I've updated MMKeyboard for iOS 5.1.1. There are slight changes in key positions compared to 5.0 due to a keyboard cache bug; not refreshing certain keys. There might be some workaround for that. But I figured it is much easier to just change key positions.
On the other note, I've set up IRC channel on freenode, #mmkeyboard. If you want to help me develop it or want to talk to me about it, free feel to jump onto that channel.