The script "grabyahoogroup.pl" works well as of May 2013. Yahoo seems to put a limit of 2500 messages. Then the script waits for several hours before continuing. I'm almost done getting close to 13 thousand messages from my group. Run with nohup on a sever or desktop. The messages are stored in individual text files that are compatible with the nmh tools.
the latest consolidated grabyahoogroup.pl script works well but is currently found only by browsing the SVN repository.