To get started see: http://msdn.microsoft.com/en-us/library/windows/apps/hh465077.aspx
For high level DirectX documentation see: http://msdn.microsoft.com/en-us/library/ee663274%28v=vs.85%29.aspx
I have been looking through the DirectX samples and have to say I am kind of glad to see C++ be combined with XAML. For too long C++ has not had a good presentation story, now it does. Excellent.
So if you want a reason to build that next killer game or simulation app then there is no better time then now.
Get Win8 downloaded, watch the videos and get into the awesome new world of Metro RT. Don’t listen to the critics, although they may have valid complaints, everything is going to get stabilized eventually. When that happens being prepared is going to make you money!