I installed Windows 8.1 today in a Boot Camp partition on my Macbook Pro. I installed the Boot Camp drivers (uses one setup file that installs a bunch of drivers). So theoretically, this HP Bluetooth Mouse x4000b, which pairs and functions in OS X, should work in Windows 8.1 as well. If I go to Bluetooth > Add a Bluetooth Device (for the first time since boot), and turn on the mouse and push the connect button on the mouse, Windows detects a mouse, and a Pair button comes up. I click Pair, and it fails. Just says "Sorry, that didn't work." Or something. I contacted HP support, who directed me to Apple, who directed me to Microsoft, who said I would need to pay for a premium support service for them to fully diagnose the problem. Nah.
So, any ideas, anyone?