Custom post types are a new feature introduced in WordPress 3.0. It is a very powerful system because it allows you to easily introduce new post-like objects, without having to write much of its associated functionality. Menus, metaboxes, permalinks, and much more can be added just by registering your new object class as a custom post type. Below are some tutorials on how to manipulate WordPress custom post types -

• Add Custom Post Type Columns
• Add a Metabox to Your Custom Post Type Screen
• Modify Custom Post Type Icons
• Custom Post Type Permalinks
• Custom Post Type Permalinks- Part 2

• Add Custom Taxonomy Tags to Your WordPress Permalinks
• Modify Custom Taxonomy Columns
• Add Term or Taxonomy Meta Data
  Describes how you can easily add new data to taxonomy objects such as tags and categories. In particular we examine add_metadata, update_metadata, delete_metadata, and get_metadata.
• Expand Your “Edit Category” Admin Panel
  We describe how to add new input fields to your Edit Category administration menu. You can then link it to new category meta-data or to the WordPress custom taxonomy system.

WordPress multisite functionality is now integrated into WordPress 3.0. WordPress multisite allows you to manage multiple blogs from a single WordPress installation; similar to the wordpress.com setup.

• Move an Existing Blog into WordPress Multi-Site
• Write a Plugin for WordPress Multi-Site