Here is Microsoft’s public announcement: http://www.microsoft.com/presspass/press/2011/jan11/01-05SOCsupport.mspx
At the same time of this announcement, nVidia has also declared that they are going to push their current ARM CPU + GPU strategy (as in their Tegra products) to the server and PC markets as well. For server markets, the lack of Windows would not have been that big of a problem anyway. HPC with GPGPU would work just fine on ARM with an alternative OS such as linux. But with Windows 8 on ARM, they may actually stand a good chance on the desktop/notebook market as well, in the future. .NET applications would run out-of-the-box in most cases, and most C/C++ applications should be only a recompile away from running on ARM. With the ARM architecture traditionally being less powerhungry than the x86, combined with nVidia’s GPU power, it could be a great option for small netbooks/notebooks. I can just imagine: a Windows notebook capable of full BluRay HD playback, reasonably capable at gaming, with the battery life of an iPad!