One of the really interesting things that's been integrated into Microsoft's Silverlight platform is Deep Zoom (previously known as Seadragon).  I got to see this a while back and it's certainly an incredible experience to play with, but the tools for generating the image pyramids that allow this to work were...limited (i.e. non-existant).  However, since deploying Beta 1 at MIX, Microsoft have released the Deep Zoom Composer application which looks very similar to the tools in the Expression Studio range.  Go check it out!