I've watched lots of Kinect 'hack' videos and I've asked myself in what way they make interaction with computers [insert positive adjective here]. Is it easier, faster, more comfortable, more practical than traditional input with mouse and keyboard (or touch)? I think in most cases I find the answer is no. If you take away the coolness factor of controlling something without touching anything and look at it from a neutral perspective the interfaces are slower, less accurate and often uncomfortable (Stretching out arms for hours? Having to hover a button for x seconds to press it?)
Kinect is good for games in which you play a character that moves in a small area (like dance, boxing, fitness). It's good for places where you should not have to touch anything (clean room, wearing gloves) and maybe for public showcases if you don't want to use a touch screen. But it won't replace mice, keyboards and touchscreens.
There are a lot of videos featuring Kinect interfaces for games. These are in most cases not natural user interfaces. Yes, you don't need a device to control your character. But it's not natural to use your arms to look or move around. In reality you use your hands to manipulate things, turn your head or body to look around and use your legs to move.
I think this is going in the right direction:
SUVIX demo - VR environnment using Kinect
Now imagine combining 3D glasses with skeleton tracking and a 2D treadmill (like this). Star Trek Holodeck anyone? The only things still missing are force fields, that let you feel what you interact with ;-)