Wow, do I share your concern. I administrate several large lists and they
are getting larger all the time. Lots of professionals too and I hate to
loose them to noise from newcomers who, as you note, don't read anything
and don't seem to get the sense of how many people are getting their
'noise' messages.
 
I did a survey at one point and the list, surprisingly, voted to a person
not to have a moderated list. Would slow down the conversation, and they
are right, of course.
 
One thing that has helped is to switch list-servers. I'm now using
majordomo, which automatically catches all the errant subscribe
(unsubscribe) messages so that they only come to me. Cool.
 
And I have become increasingly draconian. This has irritated a (very few)
noise makers, but it has kept the my lists much happpier in general.
 
-Sharon
administrator, rocks-and-fossils
administrator, women