I modified my .gnus to save sent messages into the originating group
so I can follow threads more easily:

(defun use-this-group-for-archiving () 
;; swiped from http://www.faqs.org/faqs/gnus-faq/section-29.html
(cond ((and gnus-newsgroup-name
              (stringp gnus-newsgroup-name)
              (string-match "^nnml" gnus-newsgroup-name))
         gnus-newsgroup-name)
        (t "nnml:mail.misc"))
)

(setq gnus-outgoing-message-group 'use-this-group-for-archiving)

An irritation has cropped up: the messages that I've sent show up in
the originating as unread mail. Is there any way of preemptively
tagging the Gcc: messages as read before they get saved into the
group?

--Joe