...I don't mind cels with unmatching backgrounds 
so much if they look good together, really, but I 
make no efforts myself to buy background to go 
with cels. I.e. if I got a cel with a mistmathed 
bg but it looked really good...I'd keep it. But I 
would never go out of my way to get a bg if the 
cel didn't come with one. As you can see, I'm 
really quite ambivalent towards them ^^

The only time I have a problem seeing bg's added 
to cels is when it's really tacky looking. We've 
all seen it...that cel that would look great, if 
the collector hadn't paired it up with the 
ugliest and most non-matching background on the 
face of this earth. I HATE that...I really think 
that if you get unmatching bg's, at least try to 
be close to the original scene. No sticking 
mountains in there when the characters are 
supposed to be inside.

And that's my take on the whole thing ^^

-Misha