I gather that only one copy of perl is actually loaded, am I right?

Yes, one copy of the perl compiler/interpreter and probably one copy of your Perl source code (unless you "require", "do", or other similar things at run time).

Could it be I am misleading myself about actual memory comsumption?

Yes, it is possible that most of the parent/child memory listed by ps is shared amongst them.

I tend to use the "top" command to watch the shared memory usage. It seems that ps should have an option to show shared memory, but I couldn't get it to work right off.

What really matters is how much free memory you have on the system when everything is running. Try a before and after snapshot using something like "free" and make sure to look at the free momory +/- buffers/cache.

-- Eric Hammond