Bryant has an interesting post about using ASP.NET server controls to project WPF/E XAML instead of HTML. This is a great idea and I agree that it has legs. I see this as an area of low hanging fruit for integration of ASP.NET and WPF/E. Any part of your ASP.NET page that represents a cohesive chunk of browser real-estate is a great candidate for ASP.NET XAML projection. Think chart control, video player or even data grid.
Bryant has code for the sample in the blog entry, and the sample looks great (thanks to Martin Grayson). However, there is one big UI no-no, click events fire on mouse-up, not mouse-down. Click the image below to run the sample.