Well, it's been a long time coming, but Microsoft has finally released its Windows-optimized Kinect sensor. The company made the announcement on its official Kinect for Windows blog this morning; and sure enough, the sensor can be ordered now from Amazon and the Microsoft Store for $249.99. Education customers can purportedly get a $100 discount.
What makes the Kinect for Windows sensor any different from the much cheaper Xbox 360 model? According to Microsoft, the Windows sensor "expands the possibilities for innovation with features like Near Mode, which enables the depth camera to see objects as close as 40 centimeters in front of the sensor." (That's probably handy unless you routinely sit a few feet away from your PC.) Also, you can plug as many as four Kinect for Windows sensors into the same computer.
Along with the hardware, Microsoft has released version 1.0 of its Kinect for Windows developer toolkit and runtime. That's available here. From what I can tell, developers pretty much make up the entirety of the Kinect for Windows target market right now. The Windows sensor doesn't ship with any software, and I'm not aware of any PC games that support it. That doesn't mean we won't see some cool applications—but right now, the appeal for average users seems rather limited.