I just wanted to mention that the theory that my loss of shared memory in the parent is related to swapping seems to be correct.
When the lack of sharing occurs, it is correlated with my httpd processes showing a SWAP (from top/ps) of 7.5MB, which is roughly equal to the amount of sharing that I lose. I've been lowering my MaxClients setting (from 25 to 10, so far) in hopes of finding a new balance where SWAP is not used, and more RAM is on order. Thanks -bill