With the release of Windows 8 Consumer Preview last week the path is open for developers and designers to start building Windows 8 Metro style apps. Partly for myself but hopefully useful for you too: I gathered a list of official (technical and developer) blogs to add to your RSS reader.
For developing Metro style apps the following are also recommended blogs:
The Microsoft Expression Blend team blog
The Visual Studio Team Blog: http://blogs.msdn.com/b/visualstudio/
IE Team Blog: http://blogs.msdn.com/b/ie/