An unsolicited message sent to me by someone who doesn't
even know who I am sounds like spam to me. I dislike
mass-mailings even if the sender knows who I am. I am
therefore completely opposed to being able to send
chatterbox messages to more than one person, particularly
to a group specified by some quality other than a
user-specified one (such as a list of people who all
happen to be your friends).
Why not just
make a post mentioning an event, so that those who are
interested can respond, and those who aren't are left alone?
It's worked pretty well for other events.
As for determining the distribution, maybe jcwren will
come up with something that scans homenodes and generates
a distribution map...