The 3.x branch of Drupal for Facebook requires the version of Facebook's libraries announced in April 2010. Other differences from previous branches include bug fixes, simplification of code and administration, and new features.
If upgrading from an earlier version, you'll find that basic settings, like application keys, will upgrade without problems. Other features of the 2.x branch, like feed templates and profile boxes, have no equivalent in the new Facebook SDK. So frankly these are simply no longer used, and any feature based on them has to be re-implemented.
Use the pages below to learn how to install, setup, and configure modules/fb 3.x on your Drupal website in order to integrate Facebook applications and social plugins.