Something that would make subgroups a *lot* more useful would be to
have more than one level of nesting.
A (very) concrete example: the National Assocation of Rocketry has a
group, groups.nar.org. Each NAR local club has a subgroup; my local
club is FLARE-Members@.... It would be very helpful if it
were possible to have subgroups of FLARE-members for the club
officers, for our safety committee, for our equipment committee....