Well, I just left the cel in the freezer for a 
little under an hour and pulled it out.  This 
actually worked better for me than the blowdryer 
with this cel-the blowdryer seems to work better 
on cels that aren't all that stuck.  This cel 
was S-T-U-C-K.  Majorly stuck-I would say almost 
seventy percent of the paint.  The blowdryer was 
ineffective with it (I've used it on several 
other cels with good results-never any paint 
melting ;P) 

After I took it out, the sketch came off much 
easier.  It tore a little and left some of it on 
the plastic but no paint came off.  I don't know 
how well it would work on a double layer cel...I 
have one I'm not TOO attached to...

Give me another half an hour...