As a comparison, the "Design Patterns in Ruby" by Russ Olsen (where MP 
is one of the Ruby design patterns, in addition to the standard GoF 
patterns) never suggests reopening classes as a solution to any problem 
in the book, as far as I remember. When needed, methods are added on a 
per-object level.

And David Black seem to say about the same thing as the OPs blog, look 
at page 28 in this presentation:
http://www.chariotsolutions.com/slides/pdfs/rubyeast2007-black-PerObjectBehavior.pdf


Best regards,

Jari Williamsson