Wordpress now has a cool option that allows you to make one of the pages a static front page so that your site's main look is always the same. However; in your menu, that page will show up when really, it shouldn't! If it does, you end up with two links to your main page and wasted real estate for your menu.
The solution, find (usually in the header) the
Code:
wp_list_pages('sort_column=post_date&depth=1&offset=1&title_li=');
and replace it with
Code:
$tmpexclude = get_option('page_on_front');
$tmpline = 'sort_column=menu_order&depth=1&title_li=&exclude=' . $tmpexclude;
wp_list_pages($tmpline);
That should eliminate the duplicate