User Taxonomies

This plugin extends the default taxonomy functionality and extends it to users, while automating all the boilerplate code.

Once activated, you can register user taxonomies using the following code:

register_taxonomy('profession', 'user', array(
    'public'        =>true,
    'labels'        =>array(
        'name'                      =>'Professions',
        'singular_name'             =>'Profession',
        'menu_name'                 =>'Professions',
        'search_items'              =>'Search Professions',
        'popular_items'             =>'Popular Professions',
        'all_items'                 =>'All Professions',
        'edit_item'                 =>'Edit Profession',
        'update_item'               =>'Update Profession',
        'add_new_item'              =>'Add New Profession',
        'new_item_name'             =>'New Profession Name',
        'separate_items_with_commas'=>'Separate professions with commas',
        'add_or_remove_items'       =>'Add or remove professions',
        'choose_from_most_used'     =>'Choose from the most popular professions',
    ),
    'rewrite'       =>array(
        'with_front'                =>true,
        'slug'                      =>'author/profession',
    ),
    'capabilities'  => array(
        'manage_terms'              =>'edit_users',
        'edit_terms'                =>'edit_users',
        'delete_terms'              =>'edit_users',
        'assign_terms'              =>'read',
    ),
));

Read more about registering taxonomies in the codex
This is heavily inspired by previous work by Justin Tadlock