
The good thing about it is that it may bring some competition in the Internet's high-quality, cross-platform, cross-browser, media-enabled rich interactive applications developing business.
Presently there are few options in developing streaming applications which are both flexible & internet friendly, Silverlight will bring an option for the developers as well as the user to experience a different experience.
The offer from MS is that - With the ability to author content in Microsoft Expression Encoder and other third-party editing environments, Web designers maintain complete control of the user experience.
The plus point I saw is that it supports all browsers and platform, the rest has to be tested in the coming days. Keep watching for updates!