It would be neat if you had a mailing list that didn’t actually send mail to everyone on it. Instead, it might send mail to everyone in a given zip code (yes, you’d have to give the mailing list manager your zip code), 90% of people in adjacent zip codes, 80% of people in zip codes adjacent to that, and so on. This would be geographically-centric but still deliver to a mix of people, reducing e-mail volume for folks and adding potential for creating pockets of local flavor.

You could do something similar with e-mail on a social networking service: to 100% of my friends, 50% of their friends, and 25% of the friends of the friends of my friends. This could be neat, and less overwhelming than the current setup.