I cover the Features Module (http://drupal.org/project/features)
Who: This module is intended for users that have multiple sites that use the same functionality. What: The features module enables the capture and management of features in Drupal. A feature is a collection of Drupal entities which taken together satisfy a certain use-case. When: I recommend that all Drupal users who have more than one site use this module. It is possible to use this if you only have one site and you want to use pre-created features. I also tend to use this with install profiles to limit the amount of SQL I have to write in the profile. Where: In your /sites/all/modules Why: Because having to re-create the same CCK types, settings and other things over and over again just isn't fun.
