AndroidPolice writes about WindowsAndroid, a new Android shell that runs natively in Windows without using emulation. WindowsAndroid uses the Windows kernel instead of Linux, it's currently still based on Android 4.0.3 but work is underway to port it to newer versions. You can download an early release version over here.
It allows for the full Android experience, including full support for GApps (which have to be flashed separately). It also supports a wide range of screen resolutions, and will give you the appropriate interface accordingly. For example, if you're running it in a window smaller than 1280x800, it will default to the phone interface; bump it up past that, and you'll get tablet-optimized Android.
Since it's Android 4.0+, it can take advantage of various input devices, like a mouse and keyboard for example. That's good, because most people don't have a touch-enabled monitor. And the experience just wouldn't be very good without a way to interact with it.