Post in Forums via email

Posting by emails and getting updates by emails are the two most important things IMO for a small community site, or community which does not have tech savy users or "low internet users group"

If users can post in forums via emails and get updates to the forum post in their inbox the site usage will go up a lot.

This feature is not available in many CMS and even vbulletin does not have a module to date. So Drupal has a edge here.
Modules required:

1. Mailhandler
2. Listhandler

Configuration required on webhost or mail host for.

1. Setting up a mailing list.
2. Setting up an email.

It is a bit time consuming to set it up, but its worth it. Check out the details at

http://drupal.org/handbook/modules/listhandler

&

http://drupal.org/node/40777

After successful implementation of above, a good user documentation is need to let the users know how to post in various forums on the site.

1. Easy to remember email addresses needs to be set up.
2. You need not provide functionality to post in all forums, but allowing to post in few forums will also be a big plus.