Does anyone know how to get Expression Blend to work with XAML-based Metro Apps?
The developer preview only supports HTML5 in Blend. I've tried all sorts of tricks, including installing Blend 4 on the developer preview and trying to load projects into it, but nothing works.
I would wait - there is a chance we will get something next month with Beta release of Win8. They really don't have to be tied to one another, but one could still hope.
Meanwhile the best solution is probably to Blend things in Silverlight and just copy the XAML over to the WinRT project.
Another thing to do is to learn XAML well and type most of it by hand - that is faster for most XAML activities (not assuming you don't know XAML well, but someone else who reads it might not know it). I am a big fan of WPF Unleashed for learning the foundations of XAML.