Whether your interests run to knitting or brain surgery, chances are good
other people out there share them. The new Google Groups not only helps you find
information on millions of topics; now you can actively share ideas and opinions
with others about each and every obsession of yours. And if you don't find a
group already focused on your passion, by all means start one. Invite others to
join your group so that all interested parties can read and respond to messages,
share opinions and ideas via email or your own group's web page. If you're
looking for a group to join, we could definitely use some thoughtful insight (or
idle speculation) over at my space elevator group. Shannon Bauman Associate
Product Manager, Google Groups

More here ( google.com/googleblog/2004/12/new-gaggle-of-groups-update.html )