As tidbits start to come out about Windows 8, it appears that we'll see a significant shift in the Windows UI in the next version. In itself, there's a whole lot of significance as it's a paradigm shift in terms of UI design. But from a technology perspective, I find it more interesting.
My stance has always been that aside from a few use cases (streaming media, 3D-graphics, complex animations, games), there are very few use cases that call for Flash or Silverlight.
WPF on the other hand, is a much more interesting and useful piece of technology, but even with WPF, I find that the development cycle is still slow and there are some idiosyncrasies with HTML that are hard to overcome for me (case in point is WPF Grid layout and HTML table layout).
Maybe because I come from a web background and because I've been writing web applications and building web interfaces since I was a teenager, I've always been able to build richer, more compelling, more interesting user interfaces in HTML -- faster -- than I've ever been able to do with WinForms or WPF.
So this is good news to me. Time to get cracking on those HTML5 books!