Mike's name certainly attracted immediate attention as I know him from many years using Adobe's suite of design and development tools and working on betas for new product. I came to our shop, a Microsoft Gold Partner, as more of a designer than developer, and I still use Flash extensively. Silverlight 1 and 2 offered little to convince us to switch technologies. The install base for SL is still exceedingly small compared to Flash. Our recent work on a large-scale WPF application for use in our nation's public schools has provided XAML experience within our developer team. Visual creation appeals to me more than code, so I prefer Expression Blend over Visual Studio, but I know XAML and can work in either IDE. Our Mac-oriented designer is totally committed to Flash, of course.
Now, the current requirement is to deploy secure content to thousands of schools running Windows, Macs, and Linux on all variety of hardware and connections. Everything we produce must be fully Section 508 accessible, too. I'm putting together proof-of-concept apps using both AIR and SL4 beta to see how far we can go with each. But I fear neither will capture the prize. Advancements in out-of-browser support will help tilt the scales, as will full-feature support on all three operating systems.