Microsoft have previewed Windows 8 at the D9 conference, including a video showing it off.
It seems like a slightly crazy mix of backwards compatibility and some quite cool new ideas that are meant to be suitable for keyboard/mouse based systems as well as touch based. What is interesting though is the mention that the new style tiles and apps are built on a new platform using HTML5 and JavaScript. It seems unclear what the future of Silverlight is, but what is clear is that Microsoft is definitely embracing the HTML5 world.
This can only be good for HTML5 development and tools.