Silverlight for Windows Phone is one of the most exciting things to come along since the original release of Silverlight. Now I can take my same Silverlight/WPF skills and use them not only on the web, and on the desktop, but also on the Windows Phone. Silverlight for Windows Phone is an out-of-browser, chromeless, implementation of Silverlight designed as the premier application development tool for Windows Phone. Applications written in Silverlight for Windows Phone are developed using Visual Studio and Expression Blend, and sold/deployed using the Marketplace.
from Pete Brown