After thinking about it further, if piling everything into one directory is just too gross, image caching could probably still be accomplished by putting a squid-cache in front of OpenACS. In the case I mention above, that would have been more work (the sysadmins already had a switch in place, but didn't have squid-cache installed) but certainly possible.
Or maybe an enterprising C programmer wants to see if anything creative can be done with fastpath (which, incidentally, won't run on OpenACS systems because you can't register more than one proc on "/").
