These documents provide a list of new features, changes or enhancements that have been made to Silverlight since the Silverlight 1.0 Beta release (MIX release May 2007).

In addition, they provide a list of "breaking changes" which are changes that you might need to make in applications that you created using the Silverlight 1.0 Beta to make them compatible with the RC release.

http://msdn2.microsoft.com/en-us/library/bb693297.aspx

http://blogs.msdn.com/jstegman/archive/2007/06/06/more-v-1-0-changes.aspx