Although the patterns and practices team talked vaguely about porting the Composite UI Application Block (CAB) to WPF, and about CAB being the correct architectural choice to leverage WPF in the future they are yet to release any working code. Fortunately there now seems to be a project on CodePlex devoted to just this - nice work Kent. In addition, it seems the open-source WPF media player Crescendo also includes a WPF CAB implementation.