I've because of the following arguments within the wordpress_list_groups function.

<?php wp_list_categories('show_option_all=All&hide_empty=0&title_li=&current_category=All'); ?>

I would like the 'All' choice to be visible in almost any category listing. However, since automatically, all posts load, the styling for current_category also needs to affect 'All'. However, since All doesn't have a category ID, I don't understand how to apply the present-cat class to 'All'.

Any suggestions?

You can fetch their email list right into a variable (add echo= towards the parameters), and place a custom class using string replace.

Update:

Something similar to this:

<?php 
function str_replace_once($needle , $replace , $haystack){
    $pos = strpos($haystack, $needle);
    if ($pos === false) {
        return $haystack;
    }
    return substr_replace($haystack, $replace, $pos, strlen($needle));
}
    $args = array( 'show_option_all' => 'All',
                    'hide_empty' => '0',
                    'title_li' => '',
                    'current_category' => 'All',
                    'echo' => '0');
            $str = wp_list_categories($args);

            $str = str_replace_once('<li>', '<li class="current-cat">', $str);
            echo $str;
?>