Okay, of course [slaps forehead], 135mm is certainly a decent focal length at the zoo. Close animals are not something I shoot very often, but when I do I get lost in my own little world, and I'm very glad I had the capability.
After looking at all of the posts in this thread so far, I think I would be reasonably happy to crop a 135mm to 180-200mm field of view (especially for architectural shots).
I can just imagine shoooting an old J-11 in a zoo with someone next to me hunched over a 400mm white canon lens mounted on a monopod, fretting over the light not giving him enough "feather detail", or some such....
Thanks again to everyone so far!