This is a problem I'm encountering a bit as well -
 mostly with my manga orders.

I once had a cel arrive where the cardboard box 
(like a shirt box in general dimensions) had been 
totally mangled and crushed.  If the cel had not 
been floating loose in a sea of tissue paper 
within the box (free to flex and move) it would 
not have survived.  This was an interesting 
result because it illustrates that packing 
between sheets of cardboard can be more 
dangerous.  I would have liked more layers within 
the box though - this type of box was not robust 
because it's surface area was large (and 
therefore the middle of the box had no support 
against crushing).

The original poster mentions that the parcel was 
labelled 'do not bend'.  This is a serious 
misunderstanding on the part of the senders, and 
here's why:

- The Post Office does not single out the parcel 
for special treatment because you write 'do not 
bend' on it.  They can't - there is too much mail 
to assign a personal postie to each parcel.

- A parcel will be placed randomly in a sack of 
mail of perhaps 40kg or more in weight and thrown 
from truck to truck.  The other parcels will be 
free to jab into the parcel with their corners.  
The other mail items in the sack can not read 
the 'do not bend' request, so it is ignored ;-D

In conclusion, a parcel with a fragile and rare 
item should ideally be packaged on the assumption 
that it will have a 40kg weight of indeterminate 
shape dropped on it.  In practice, most parcels 
will survive with less - but it is a calculated 
risk that is being taken with something treasured.