Many features of powerful data-driven sites used to be implemented as Nodes in Drupal: Media, Social Networking, Groups, eCommerce, to name a few. These days, the Node is being unseated as the most powerful structure in Drupal site building.
Drupal 7 introduced a new layer of abstraction - Entities.
We are familiar with Nodes and Content Types, and all the power and flexibility we got from those in past versions of Drupal. However, adding new data models was not very attractive in old versions because of the power of tools like CCK and Views - Nodes were the king of all data types.
Now Entities allow us to (somewhat) easily create new entity types or add "bundles" to existing types, and all Entities may now also have "Fields", which is the new name for CCK in Drupal Core. In this session, you'll get a brief history of some old-school solutions to common problems in Drupal, and the modern Entity-based solutions based on Taxonomy Terms, Users, Comments, Media and new types as-of-yet unimagined.