One of the things that I really thing would be important for Silverlight in order to make easier the Modularity of the Business applications developed in Silverlight, since the Prism approach is nice but I think that the MEF approach is simpler...
Silverlight 3 has been release and now we have also the Unit Testing Framework binaries here that will help making Unit Tests in our solutions when using Silverlight 3. More information’s here . Also important is the release of Prism Visual Studio Templates...