A succinct Silverlight summary from Brian Goldfarb, in the comments thread for a Bob Muglia post clarifying his PDC comments about Silverlight’s role; see the link below for more context-setting and details
Silverlight is definitely alive and well and goes far beyond just WP7. I think that is pretty clear from Bob's post, but I'll reiterate it again. Silverlight will continue to be invested in across the board. It is the way to build Apps for Windows Phone 7, but it is also and will continue to be the best solution for premium media experiences and business applications both inside and outside the browser on Windows and the Mac. The key thing that has been clarified, is that we see HTML as the technolgy that gets you *everywhere*. In fact, for the broadest reach today the solution you should use is HTML4. But if want a richer, more tailored experience, on the devices and areas we support (and we are investing in this with Windows Embedded, Automotive, Desktop, Phone, and more in the future) both in and out of the browser than Silverlight was and continues to be your best solution.