Well actually, though I have no graveyard done 
at the moment, I think it is a very interesting 
idea as long as it is clearly stated 
as "graveyard" or other words stating that the 
cels are not owned by the person anymore.

Personally I don't mind, when buying a cel to a 
private collector, that (s)he keeps a track of 
it on his (her) gallery in the graveyard.

We are all pretty fond of our cels but we also 
love to share them, isn't it? If not, why do we 
do cel galleries? Just for the evil pleasure to 
make others jealous? Of course not!!! So, I 
think we should also share our beloved cels with 
the people who offered us the opportunity to get 
them...

Just think about this last sentence...
Cheers