The Getting Involved handbook project has been in the works since March 2008. For background on this project, read the Drupal.org front page post.
The current status is that we have done the initial creation of the book and added it to the Documentation landing page (as of September 28, 2008). It can be found at http://drupal.org/getting-involved. Now that the book is created we need to finish it up. Currently the landing page has a list of high-priority issues to finish. You can also see the remaining issues in this issue queue search.
Beyond finishing the specific issues (which mostly involves finishing a few incomplete pages), we also need folks to read through the book and identify places that don't feel like they are in a good order or where the information doesn't make sense. We also need to think of things that are missing and should be added to help people get involved in many ways. If you find problems or have questions, feel free to create a new issue in the Documentation issue queue and/or just jump in and start editing.