The best place to ask about silverlight is www.silverlight.net
Anyhow...I notice a very interesting comment you made: "microsoft doesnt have powerful designing tool...like flash"
Have you heard of expresson studio, or more specifically expression blend? Expression blend makes deevloping WPF and Silverlight design a breeze. The main concern about silverlight is market penetration, which stands at about 28%. The market penetration is increasing everyday, and some major events are being covered by silverlight. As a result silverlight penetration will keep increasing.
One major benefit of silverlight is that you use existing development languages with exisiting tools like VS. Also, the VS + expression combo enables your designers and developers to work together seemlessly. Tooling support for silverlight is trully awesome.
Silverlight (from 2.0 onwards) features a mini .net runtime that runs on the browser. It is not interpreted code. It's compiled code and runs very fast.
Silverlight supports h264 encoding for video, and can be used for live streaming. This is something that the flash world can't do. This is one reason that google used silverlight to display a live event instead of using their flash player.