I have framed about 15 of my anime cels over the 
past year and believe that if you are careful, 
use the proper materials and keep the cel out of 
excessive heat and direct sunlight, it can both 
enhance the beauty of the cel and make it easier 
to enjoy, cuz it's always there on the wall.  

Between 1984 and 1988 we bought a bunch of framed 
Disney and Warner Brothers cels (both production 
cels and repros), which have been on our walls 
most of the time since then, and I really don't 
see any line fade (although there is some warping 
in a couple of them).  Could be that the paints 
and the process for creating the lines in the US 
are somehow more stable than those used for 
anime.  

If anyone's interested, I can email or post a 
brief summary of the materials I use and how they 
go together.  After an initial outlay of about 
$100 for a mat cutter, I can double-mat a cel in 
a wood frame using archival materials for about 
$15 (or higher if I want a fancier frame).  Note 
that it's only that cheap if you want to frame a 
number of cels.  However, even my wife thinks 
they look nice (although I still can't figure out 
why she tolerates pictures of women she doesn't 
know on her walls).   

I just can't imagine keeping nice cels of 
Belldandy and Ryoko stuffed in cel books.  

My 2 cents.  

Jim