Don't get me wrong, I love my ferrets.  I have six and they probably
won't be my last.  But, in comparing them to my other pets, these are the
downfalls I see:
 
Expense--ferrets and the initial setup are far more expensive than
rodents, rabbits, and similar pets.  High quality food and bedding are
expensive, and they require yearly vaccinations.
 
Medical Risks--ferrets are prone to a number of serious illnesses that
are difficult to prevent and expensive to treat.  These include both
cancers/genetic diseases and accidental injuries.
 
Destructiveness--ferrets love to dig, chew, hide, and make a mess of just
about everything.  They are likely to demolish at least a few things in
every household.
 
Predatory Behavior--ferrets, for the most part, cannot be kept near birds,
rodents, reptiles, fish, etc. because they see them as prey and/or play
too rough.
 
Public Perception--just having ferrets can dissuade people from visiting
you if they are under the impression that ferrets are smelly or malicious
animals.  Ferrets require almost constant defense.  It's also hard to
find veterinarians that are ferret knowledgeable, and you may have to
order supplies that your local store doesn't carry.
 
Dependency--ferrets are time consuming and demand lots of exercise and
attention each day.  They cannot be left alone for even a short trip
because of the risk they will spill their food or water.  Once obtaining
a ferret, you are responsible for feeding, cleaning, and exercising the
pet every day, even if you are busy or sick yourself.  It's a major 8-12
year commitment to make.
 
Maintenance--ferrets can't be expected to defecate outside like a dog,
and although they can be litter box trained, they are rarely perfect.
Cleaning up after a ferret is a frequent, unpleasant chore.  They also
require nail trimming, ear cleaning, teeth brushing, bathing, and laundry.
It is not as simple as dumping a hamster cage.  They also have to be
trained and socialized.
 
Independence--for all the work you put into caring for your ferret, you
might not feel like you're getting much back.  Although they love their
caretakers and sometimes want to play and snuggle, they don't have the
unconditional devotion of a dog.  Their primary interest in life is not
to please you.  Most don't want to just curl up on your lap while you
watch t.v. and they have to be constantly supervised for their tendency
to climb up higher than they can climb down and eat undigestible things.
[Posted in FML issue 3700]