A new version of Silverlight 3 has been released.
You can download the latest control here. If you are a developer, then you'll want to use the developer installer that is available here.
This version fixes some issues related to hardware acceleration in the graphics processing unit (GPU), certain cases that cause Deep Zoom to take on high CPU, and issues with downloads from Silverlight applications.
Read Microsoft's Knowledge Base article for this release: Description of the update for Silverlight: January 19, 2010.