The main attraction in this release is the new admin screen that gives an overview of all the connection types found in the system:

Connection Types screen

Another thing to note is that queries like this no longer work:

$query = new WP_Query( array(
  'connected_items' => get_queried_object_id()
) );

You have to set the ‘connected_type’ parameter:

$query = new WP_Query( array(
  'connected_type' => 'posts_to_pages',
  'connected_items' => get_queried_object_id()
) );

Also, you can pass an array of connection types and P2P will pick the ones that make sense.

$query = new WP_Query( array(
  'connected_type' => array( 'posts_to_pages', 'actors_to_movies' ),
  'connected_items' => get_queried_object_id()
) );

As with every release, it contains a bunch of smaller enhancements and bug fixes. See the changelog for more details.