We want to implement a feedback system for services (these would be CiviCRM Contacts). Think of it like eBay feedback with an overall rating and some sub-categories like speed of dispatch, comms, description of item, etc.
Each of these ratings would be stored as a Custom Field against each Contact.
Feedback would be gathered via Activities. Could Civi or Drupal Rules be used to calculate averages (based on multiple Activity submissions) and update the custom fields on the Contact?