Without a doubt, one of the largest web sites I had the pleasure of working on. Perhaps not always a pleasure as things were crashing often in the "early days." Originally built on WordPress then moved to Drupal (before I touched it), and then I braced it with CakePHP. A lot of the galleries I built for the site were CakePHP applications built to co-exist with Drupal which allowed the site to quickly produce several types of galleries (some with voting, etc.). It also helped the site scale much better than Drupal. The end result was a very adaptable, though confusing, codebase which did change very frequently due to client request. Eventually the entire thing was cached using Akamai and then later rebuilt with Symfony for everyone's sanity. It was a wonderful experience for understanding how to deal with hundreds of millions of pageviews per month on a frequently changing and feature demanding site.