The Wilderness Within
This was one of our very first Drupal projects, so old in fact that it was done on a dev version of Drupal 4.6! We're quite proud of the site and work done on it, especially the theming. The Wilderness Within site had been chugging along nicely for a good 4 years until one day the admin section stopped working. It turns out that the hosting company had updated their PHP version which was no longer compatible with such an old Drupal release.
Garret and Will, the founders of the company, contacted us to troubleshoot and fix the problem. We made a few small fixes so that they could log in and update some content and then recommended that they upgrade to a current version of Drupal. Given the site's age and condition we had to decide whether it would be best to upgrade the site from 4.6 --> 4.7 --> 5.x --> 6.x or to just rebuild it with a fresh 6.x install.
Given the availability of modules such as CCK, Views, Panels, Calendar, Date, Imagecache, etc., as well as the age of the theme, we determined it would be best to rebuild it rather than upgrade. We started the process and a week later had the new site approved and pushed to the production server. We were very happy to see one of our first Drupal sites get a new life and our client was happy to have everything working again and fully up-to-date. Next time they aren't going to wait 4 years to update the site!