The Database Health Report provides you with a snapshot of your CiviCRM database's usage. It reports the last login time and number of contacts and activities modified by each user. WIth this report, you can evaluate the effectiveness of staff trainings, or get a quick glimpse into which users are active and who may need more prodding.
Note: this is packaged as a native CiviCRM extensions, however, it includes queries that depend on Drupal's user table.