Has anyone found a good way of using the new iOS5 keyboard events?
The thing is not to overthink this. Nothing of any importance has changed. If the keyboard comes into docked position at the bottom of the screen, you will get a "show" notification. If it leaves the docked position at the bottom of the screen, you will get a "hide" notification. That's exactly what happened before iOS 5.
The only difference is that instead of leaving the docked position because it is moving offscreen, it might be leaving the docked position because the user undocked it. You'll still get a "hide", so you can move your interface back into its base position. You don't need to know that the keyboard is now undocked (though you can find out that it is not offscreen from UIKeyboardDidChangeFrameNotification if you really want to). The reason you don't need to know is that when the keyboard is undocked / split, the user can be proactive and move the keyboard if it's in the way of something that needs to be seen.
Thus, all your old code from before iOS 5 continues to work just fine. It's all really quite clever...