While Layout Persistence has been announced as a new feature in 2010.2 release of the Silverlight Toolbar and Menu Control library, it has been available in the WPF version of the component since version 2010.1. Check out the following video tutorial that demonstrates how to implement layout persistence in the WPF Toolbar and Menu Control as well as how to load existing layouts saved as XML files.
The complete project for the video is also attached at the end of this blog post.