Tim Anderson attended Joe's session at Mix '06 and spoke with Forest Key, Director of Developer Tools Product Management at Microsoft.  His article can be found here.

 

One of the best insights Tim has is the complimentary nature of WPF/E's two programming models.  The .NET programming model makes it easy to create your app by leveraging the tools, samples and expertise that has built up around managed code over the last 6 years.  The javascript programming model provides the glue to seamlessly integrate your app into the browser.  Through javascript, your WPF/E app can access and modify the HTML DOM of a web page.

 

On top of this, WPF/E provides UI through the vector based, designer friendly, media integrated UI XAML format.  And of course the great tools in the Expression suite will edit the same project files the developers code against in Visual Studio.  Taken as a package, we think this is very exciting stuff.