Angus Logan asks:

• Do you have media like *.mov files which Silverlight doesn't speak?
• Do you really really want that media in Silverlight?
• Do you have an abundance of bandwidth to push un-encoded files up to the cloud?
• Sick of melting your CPU to encode media? we can do it in the cloud.

On his site you'll find a video demonstration of the experience and details on the coming API's.  This isn't a replacement for Expression Encoder, rather I see a compelling service for everything from next-gen ad solutions for customers  looking to ingest a myriad of formats into standard video formats for broad distribution, to design/development houses looking to use Silverlight Streaming as a service for video delivery.  Congrats to the Silverlight Streaming team!

Learn more here.