CCK has been significantly reworked for Drupal 6, both to add new functionality and to provide stronger and code and APIs. We've tried to respond to many of the things that were often requested but were difficult or impossible to do in the Drupal 5 version: streamline the process of creating fields, use drag-n-drop to reorganize fields and values, provide a user-friendly 'Add more' button for multiple values, give developers an API and more tools to customize CCK behavior, and provide more documentation.
Many of the things you see in the latest code would not have been possible without all the new Drupal 6 and Views 2 features. Drupal 6, CCK 2 and Views 2 make a great combination!
Important: This release fixes a (minor) security issue that was present in the previous RC releases.
See the Security Annoucement for more informations.