We've been investigating using Drupal as an extranet, a site that clients can log into and see the progress of their projects, including images and photos if needed. You'll find a lot of questions from folks looking to do this, which is great, but the trick to it is pulling all the bits and pieces together and managing to build a site that is easy for the owners to manage, and easy for their clients to use. As we make progress on this, we'll try to write up what we do, and hope it can serve as a guide for others.