The Cloning 16 social media sites in Drupal made it's way back to me again. While it doesn't provide step-by-step instructions, it does illustrate what a modular CMS like Drupal is capable of. High level functionality for sites like Facebook, Digg, Tumblr, Twitter, Amazon, Blogger and Youtube can be architected an hour or so. A proof-of-concept prototype could be done in a Webcast*.

This shows that Drupal can be seen as a web application framework.

*Non-develoers may not be familiar with the sometimes tremendous difference between a prototype and a production project. The best way to learn that difference is to build a Web site!