Commerce Product Entities: 175,000+
Eurocentres is one of the leading organizations within the language travel industry. Eurocentres is an international company with schools located on four continents and students coming from over 120 countries. Currently, Eurocentres teaches eight languages at 30 schools.
We noticed that several people involved in e-commerce projects with Drupal 6 and earlier (in particular ubercart and ecommerce) started working together on a new project called Drupal Commerce (which is based on Drupal 7). That means a lot of e-commerce knowledge was brought into one single project. Drupal Commerce was in a very early stage (pre-alpha) when we decided to use it for our project but it's architecture turned out to be very flexible.
Even though we wrote quite a few lines of custom code for the shop, especially to create date based behavior, we were able to do a lot of customization by using rules and views thanks to the seamless integration of Drupal Commerce with those modules. For example: The shopping basket consists of views. Additional fees such as high season, enrollment and many other fees are calculated and added by rules. Products like courses or accommodations are stored as commerce products, each representing a different product variation (e.g. accommodations with different meal plans: half-board, full-board).
Full sitebuilding writeup here : http://drupal.org/node/1121326