Microsoft has announced that over 40 new features will be added to Silverlight 5, which will be available in the first half of 2011. The announcement came at today's Silverlight Firestarter event. You can watch the keynote here. New features announced include: support for running Silverlight applications with desktop features in the browser, text enhancements, a GPU accelerated 3-D API and more.
A demo of the new 3D API
The performance and graphics improvements include:
The full list of new features is available here.