Yesterday Cynergy, one of the top Flex development firms, announced that they will be jumping into Silverlight development. They are the first major RIA development firm I know of to publically put support behind Silverlight. A lot of the design agencies have been working with Silverlight for a while, but Cynergy focuses more on building full applications using RIA technologies. For a examples of their applications, you can check out the showcase.
Like Danny, I think this is a pretty good move. I don't think there is any doubt that Silverlight is here for the long term, and the companies that get involved at the beginning will be able to help shape the direction of the product and push the envelope when creating experiences on top of the platform. At a basic level, it's just another tool in the belt, but I do think it's significant that a company like Cynergy, which is well known in the Flex world for their applications, sees opportunity in Silverlight.