In WordPress 2.3, the new taxonomy API was introduced. It allowed us to make up our own taxonomies. Here’s the problem: No one has been using custom taxonomies.
In WordPress 2.8, creating custom taxonomies won’t even be the job of a plugin developer. Average users can make and use any taxonomy they want with a few lines of code. WordPress will handle the rest by adding the meta boxes on the write post page and new admin menus for managing them.
URL : http://justintadlock.com/archives/2009/05/06/custom-taxonomies-in-wordpress-28