Discontinued, you should look at https://github.com/danielamitay/DAKeyboardControl which does it much better nowadays.
Caveat: this has not been put in production code. Apple may deny this.
This is a working implementation of how you can create iMessage style receding keyboards by grabbing the keyboard through the view hierarchy and dragging it around. Originally started from this stack overflow question iMessage Style Receding Keyboard in an iOS App it was eventually turned into a blog post on my website, and finally this repository.
Released under BSD license