Seeing a post about Gainax and cel theft together 
in one thread reminds me of their early work, 
Otaku no Video. They would intersperse animated 
segments with interviews with "real" (and often 
kind of creepy) otaku. One of them was a cel-
thief who talked of the whole process. He said, 
first off, it was taboo to steal any cels that 
had not already been shot. Then he began to talk 
about how easy it was to just walzt into an 
animation studio and walk out...because for each 
project, so many new and individual 
animators/etc. are hired, it's hard for anyone to 
really keep track of everyone. So, apparently, if 
you choose the right time (say when everyone's 
returning from lunch) and the right company, 
people would just walk in and take cels. I dunno 
if this was how it worked for Disney (much 
tighter security, I woul imagine), but just 
thought I'd put in my little bit of knowledge in 
this category ^_^

Ja!

-Misha-chan