david:
  

   Ah... so the secret is in the hidden variables.  On some
   level I am beginning to fear that Monads resurrect some of
   the scariest aspects of method overriding from my OO
   programming days.  Do you (all) ever find that the ever
   changing nature of >>= makes code hard to read?
    

You always know which monad you're in though, since its in the type.
And the scary monads aren't terribly common anyway.