Good example of Natural User Interface (NUI)

Windows Live Messenger version 2009 change your scene, peel off effect

Recently I've just upgraded to Windows Live Messenger version 2009, and just started realizing this peel off effect at the edge of the panel to 'change scene'. I think this is a simple yet effective example of Natural User Interface. I know it isn't revolutionary, but I'm just fascinated how the WLM team paid so much attention to this.