Site Audit includes a number of comprehensive reports, each consisting of one or more checks.

We organized the usability issues into four different layers: conceptual, flow, terminology, and interface. In this document we explain what each of these means, and provide key examples and quotes from users. We also propose a quick and concise up-to-speed aid that welcomes users on a new Drupal installation.

see also: http://drupal.org/node/1427940