I have 5 babies living in a relatively small house.  Mine just DO NOT smell.
If you pick them up and put them right next to your nose you can smell them.
And the best description I can give is a sweet curry smell.  But my house does
not smell, my clothes do not smell, etc etc.  We wash them a couple few times
a year when deemed necessary.  They are descented.  2 males, 3 females.  Their
litterbox doesn't even smell.  When the boys were very young (3 months old)
they smelled a little stronger - but nothing anybody would notice without
picking them up and taking one big, concentrated whiff.  No one has ever
commented to me that my house smells or that i smell, etc.  Ours run free -
but of course have their favorite spots where they can always be found.
Sometimes, when one is very young or if one is sick or for whatever other
reason, we need to confine them to a cage the smell gets a little stronger I
suppose because it isn't dispersed throughout the house.  We have the
confinement cage in our bedroom - and in this room we have an air cleaner &
negative ion producer (1 unit).  This removes odors & particles (including
bacteria) from a room by making such substances heavy &/or sticky making the
particles causing odor to fall from the air as dust or stick to the walls.
This should help with ferret odor.  There are a lot of pros & cons regarding
them though.  I believe that negative ionization of room environments
wholeheartedly good.  Some people believe it makes their walls dirty, etc.
Another suggestion is a candle.  We bought a candle at an earth store which
you burn for a couple hours a day and it is specifically designed to remove
pet odors from your home.  We rarely use it but it has come in handy.  I think
it was called the Pet Smell Candle.  The ionizer we bought covers 600 sqft and
cost about $200.  The candle has lasted about 5 months and was around $8.  (I
actually bought the ionizer for me not the ferrets as it is touted to improve
sleeplessness and allow clearer brain activity, blah blah blah....)
[Posted in FML issue 1122]