To add another bikeshed color to the discussion, there's RForum which powers http://www.ruby-forum.com - there are some pretty high-traffic mailinglists centralized and it works very well.
You set it up and have it subscribe to any mailinglist (i.e. no need to move to Google groups). It will then act transparently as a gateway to the mailinglist.
-- sven fuchs svenfuchs@artweb-design.de artweb design http://www.artweb-design.de grünberger 65 + 49 (0) 30 - 47 98 69 96 (phone) d-10245 berlin + 49 (0) 171 - 35 20 38 4 (mobile)