Silverlight 2 Beta 1 - Online Game and the Pain it Caused
The Good News
First off, I have to say that I have successfully made an "online video game", with Silverlight as the game client. I can't stress enough how overly difficult this was, and how many "the right way" paths I went down that completely failed.
Here's the rest of my rant, including the frustrations that you'll likely want to know about if you're going to get into Silverlight: http://www.singingeels.com/Blogs/Nullable/2008/04/05/Silverlight_2_Beta_1__Online_Game_and_the_Pain_it_Caused.aspx