Hello Tom et al:
Of course there is no single answer!  What this whole discussion on
speciation has vividly demonstrated is the one essential concept we
need to keep in mind when dealing with any classification system - it
is essentially subjective.  The concept of "species" is not something
inherently present in living organisms, like the molecular structure
of a chemical compound.  Species, subspecies, families, etc. are
human intellectual constructs, set up to help us deal in an efficient
way with an otherwise impossibly complex mass of information.  They
exist as electrochemical impulses in our central nervous systems, not
as objective realities in nature.  If a pharmacist picks up a bottle
of pills and says "is this aspirin?", he can expect an unequivocal
yes or no answer.  Unfortunately, some people tend to approach
questions of  biological classification in the same rigid way - "is
this a species or isn't it?".  However, this question has no simple
or definitive answer because, unlike the aspirin question, it does
not deal with the inate identity of something, but rather with human
ideas, interpretations, and decisions regarding the position of an
unbelievably complex entity within a far more complex overall scheme.
 Aspirin is aspirin because of it's intrinsic nature - its separation
from other compounds is objectively definitive.   However, a genus is
a genus only because someone has created it mentally, and declared it
to be a reality, thereby drawing arbitrary lines of separation
between it and other similar genera.  Taxonomic questions are more
akin to a different question the pharmacist might ask - "where in the
store should the aspirin be located?".  Most would probably place it
with pain relievers;  others perhaps with cold and fever medications;
and maybe a few would put it with blood thinners and heart
medications.  None of these alternatives is wrong - they are all
subjective decisions based on observed objective properties of the
entity being classified.  Tom's example of the relocation of the
genus Morum from Cassidae to Harpidae is a tough pill for me to
swallow too.  But the important thing to remember is that neither
classification is inherently correct or incorrect - someone, after
due consideration, just moved the aspirin to a different shelf.
Because this is the very nature of taxonomy, there cannot be, and
never will be general agreement on classification.  But we could
minimize our personal need for blood pressure medication by avoiding
the question "is it or isn't it?", and instead just asking "where
should this be placed, in view of the most reliable current
opinion?".
Paul M.
Rhode Island