RIA, .NET and Xamlon
When considering your RIA options with .NET, you want to code in a language you know and use and using a IDE you know and use (debugger, intellisense etc). The XML syntax you want to target has a long term future in the Microsoft development and business world so you opt for XAML but you want to target Flash. Seems like Xamlon is a perfect match, sure Jesse has outlined some of things that need working on, but its a beta and things can only get better in a beta.