I'm using Views 3 and created a view which would show users flaged by certain user. I've read that you must select 'Any User' in relationship, but it did not work. Only possible arguments are Content ID and Flagged time. So my solution was to add the 'argument' in flag.views.inc like so and now it shows up and it works:

$data['flag_content']['uid'] = array(
    'title' => t('User'),
    'help' => t('The user that flagged an item.'),
    'relationship' => array(
      'base' => 'users',
      'handler' => 'views_handler_relationship',
      'label' => t('Flag user'),
    ),
    'argument' => array(
      'handler' => 'views_handler_argument_numeric',
    ),
  );

Is this really missing, or am I doing something wrong? I did all posible relationships but I did not get User argument. On my previous project I used Views 2, and as I remember there was no problem with this.