I've just checked in version 2009.11.11 of the SoapBox Core code and Pin Ball Demo into the public repository.  I also updated the documentation wiki to reflect the changes:

• All contract names use hierarchical string constants now instead of hard coded strings.  Makes finding extension points a lot easier, not to mention finding things that have extended certain extension points.
• Documents and Pads are now Lazy-imported, and only instantiated if necessary.
  
  
• Made changes to allow recomposition, in preparation for a planned add-in manager that will add extensions "on the fly".

I will update the CodeProject article within the next few days to reflect the new version.