I've had a cel (Miyu OVA) shipped in a bubble 
mailer with no additional protection.

I also had a cel (El Hazard, Wanderers) shipped 
in cardboard, but the cardboard wasn't snug 
against the cel at all. So the cel was freely 
sliding around inside the package. (It wasn't 
even in a cel bag. o_0;;

One of Yann's boxes (carrying a YuYu Hakusho cel) 
arrived crushed flat. Thankfully, cels are flat 
themselves. ^_^;  (But I was mad since I had 
wanted the box too. ^_^)

I had a box from Japan arrive so badly beaten, the
*hard plastic case* the seller had shipped the 
cels (Trigun) in was cracked. O_O I was very 
thankful this particular person was an overzealous
packer.

But the funniest (only in retrospect) packing job 
was done by the person who packed my cel 
(Transformers) only *styrofoam peanuts*.  o_O;;; 
No cel bag. The little pieces of peanut had lots 
of fun static-ing to the cel. ~_~

Otherwise, amazingly, all the above cels arrived 
just fine. ^_^  The only cels that have arrived 
to me damaged were damaged before I bought them, 
so I guess I'm lucky too! ^_^  (*runs off to find 
some wood to knock on!*)

Many Sharp Smiles,
--Drac