Hi @Edward:
This is not a generic solution but will probably solve your needs. If you want to get rid of the '| Portfolio Categories'
from your site’s title just hook the 'wp_title'
filter in your theme’s functions.php
file and remove that from the title string. Copy this code to the bottom of that file and modify as need be:
add_filter('wp_title','your_wp_title');
function your_wp_title($title) {
$title = str_replace('| Portfolio Categories','',$title);
return $title;
}