I used to keep them in my room...but, well I 
don't go in my room to do anything but sleep. So, 
they collected dust and got all neglected, and so 
they migrated downstairs, into the computer room. 
Why? Well, 1), it has the most controlled 
temperature in our house. 2) They're close to the 
scanner or if I ever find myself dreadfully 
unhappy with a scan, or perhaps forgot to scan a 
sketch or something, or just need information on 
cel layers and such for website coding, they're 
right there. And 3), whenever a webpage is taking 
particularly long to load or something of the 
like (slow downloads, etc), I can just flip 
through them =^.^= Then I hang them back up (I 
use the hanger method) on the various doorknobs 
around the room (one on the video cabinet, one on 
the desk cabinet, one on the door...then I have 
an over-sized celbook, but it really does live 
upstairs right now since it only has one cel in 
it).
Generally, if I really like one I tend to stare 
and stare and stare at it...and then stare some 
more...once my feet fell asleep when I stared at 
one cel too long ^^;; 

Although, Drac's comments inspired another thing 
I've always been wondering..how does everyone 
organize their celbooks? Like Drac, I too enjoy 
re-organizing bits of mine whenever I get new 
cels (in fact, on Sept. 11 I got my Eros OP cel, 
and to calm myself I found that I organized my 
whole entire cel collection over again, using the 
fact that I had to add him as an internal excuse 
for why I was doing it), but I organize mine 
differently. I leave my favorite character from a 
series, and generally favorite cels, for last, 
and try to make a running thread, like "Noelle 
cels" to "Noelle with Yuusuke" to "Yuusuke with 
friends" and so forth...try to add some type of 
continuity. In my Misc. celbook, I go by which 
number of cels per series, and if I have the same 
amount from one series I go with what's most 
aesthetically pleasing when flipping through the 
book. 

-Misha