Sebastian is on a roll! Here's another quick video showing how to customize pie menus in the upcoming 2.72 version.
In 2.72 there will be a new UI feature, which enhances user interaction in Blender: Pie Menus.
The backend has been implemented in C (thanks to Antony Riakiotakis!), but the actual pies can be easily written in Python (Pie-thon, huhuhu...). Here's a quick guide how you can setup your own menus!