Mailman is of course. As well as redhats anaconda installer and google uses python internally for many of there "medium sized" projects. Also, calibre, gwibber, portage pms, ubuntu software center, YUM pms and many others including YouTube. Moral is many big companies do both for products and internally.
Cheers, - Braden Faulkner -- http://mail.python.org/mailman/listinfo/python-list
