Windows 8.1 released last week. I knew that it was to include Miracast support, so I was pretty eager to see if it would work any better (and by "better", I mean "at all") than Miracast for the Nexus 7. I was also hoping that it would work so I would no longer have to use outdated drivers just to have Intel WiDi working on my laptop.
I installed the current Intel Windows 8 WiFi driver and the brand new Windows 8.1 Intel display driver, then connected to my Netgear PTV3000. I haven't been able to test extensively, but so far it actually seems to be working! It works OK, but it is still not as good as AirPlay. Video was fairly smooth, but the audio would occasionally stutter.
To get it working, make sure your Miracast receiver is connected to your television/projector and ready for connections. Bring up the "Charms bar" (move mouse to top right corner of the screen), select "Devices" (or Windows Key+K), select "Project", and click "Add a wireless display". After selecting your receiver, you will be prompted for a PIN that should be displayed on your television/projector. You only need to go through this full process the first time.
To connect/disconnect/configure a wireless display after the first setup, use Windows Key + K and click "Project".