In this example I will demonstrate the difference between how ExtJS 4 and Sencha Touch 2 config systems treat non-primitives (i.e. arrays or objects). This aspect of the frameworks is very important to distinguish as it will save you from some very painful debugging sessions.
Long story short, Touch will actually clone any objects from the config for every instance of your class, whereas ExtJS will slap them on the prototype (probably not what you want).
Now for a practical example.