How can I exclude a category from the main loop with the category name & not ID?

You directly cannot pass the name or slug for excluding a particular category. You have to use the id.
Modifying your code:

<?php
    $category_id = get_cat_ID('featured');
    //if get_query_var('paged') doesn't work, then try using get_query_var('page') in the next line.
    $paged = (get_query_var('paged'))?get_query_var('paged'):1;
    $q = array();
    $q['category__not_in'] = array($category_id);
    $q['paged'] = $paged;
    query_posts($q);
    if (have_posts()) : while (have_posts()) : the_post();

    the_content();

    endwhile;
    endif;
?>

Hope this helps!