The hackers claim that pretty much everything works, from WiFi to BlueTooth to GPS, and that only the graphics driver seems to have issues - there's noticeable lag in the user interface. The people behind it are planning to release a beta ROM to the public soon, which would mean that HD2 owners can run Windows Phone 7 Series before everyone else on a device that's not expected to get official support at all.
Since the internet doesn't believe stories like this without any proof, here are two videos showing it all off.
This is pretty impressive work, and shows that the HTC HD2 is fully capable of powering Microsoft's upcoming release. Since the HD2 is supposed to become available with Android too, and by default comes with Windows Mobile 6.5, the HD2 looks like a nerd's dream phone.