> I don't see an equivalent flag for a user of "do not allow posting".
> 
> Is anyone else using Mailman to handle announce-only lists like this?
> What configuration have you used?

Add the addresses to 

   http://www/mailman/admin/listname/privacy

under the "Addresses of members accepted for posting" section.
Make sure that "Restrict posting privilege to list members" is
set to no.  To quote the online help:

   o If member_posting_only is 'yes', then entries added here will have
     posting privilege in addition to list members.
   o If member_posting_only is 'no', then only the posters listed here
     will be able to post without admin approval.

> Related to this, one of the lists has about 70,000 members and is
> generated prior to posting from an SQL database.  Does anyone have a
> command-line utility one can use to *replace* the current users list
> with those from a file?  It seems to me that the users are stored in a 
> db file...

Look in $prefix/bin for the add_members, list_members, and 
remove_members scripts.  These allow you to modify the list
membership via a commandline interface.  To replace the
current users, you'd have to 

   list_members listname > /tmp/list.out
   remove_members -f /tmp/list.out listname
   add_members -n newfile -w n listname

For some reason list_members fails for me with the -o flag
(creates an empty file, then spits to STDOUT), so I redirect
to the fie.

Chris