We haven't added much lately. The reason is that Silverlight 4 will add most of the additional things we wanted to add. The main thing that SilverlightDesktop provides is "injecting modules into movable re-sizable windows with drag and drop between them" is still valid and the current program does that.
It also does that with a small amount of code. We decided not to implement the code to make the windows look better because it would have doubled the code base.
At this point we believe that SilverlightDesktop provides a useful resource in a small package.