Jesse Liberty has three great posts in which he explains about some new things in Silverlight 3 - Validation, Based-on Styles and Perspective Transforms.
In addition to the transforms that were available in Silverlight 2 (translate, skew, etc.) you can now apply perspective transforms to any Silverlight Element to create 3D images and animation.
We have a two part video on how to do this on Silverlight/Learn.