An slight mod of wp_list_authors to optionally add a class to the current author in an author archive.

sd_list_authors.php

<?php

/**
 * List all the authors of the blog, with several options available.
 * Edited to optionally include current-author class on author archives
 *
 * <ul>
 * <li>optioncount (boolean) (false): Show the count in parenthesis next to the
 * author's name.</li>
 * <li>exclude_admin (boolean) (true): Exclude the 'admin' user that is
 * installed bydefault.</li>
 * <li>show_fullname (boolean) (false): Show their full names.</li>
 * <li>hide_empty (boolean) (true): Don't show authors without any posts.</li>
 * <li>feed (string) (''): If isn't empty, show links to author's feeds.</li>
 * <li>feed_image (string) (''): If isn't empty, use this image to link to
 * feeds.</li>
 * <li>echo (boolean) (true): Set to false to return the output, instead of
 * echoing.</li>
 * <li>style (string) ('list'): Whether to display list of authors in list form
 * or as a string.</li>
 * <li>html (bool) (true): Whether to list the items in html form or plaintext.
 * </li>
 * <li>current_author-class (string|boolean) the class to highlight the viewed 
 * author with on an author archive. False will disable.</li>
 * </ul>
 *
 * @link http://codex.wordpress.org/Template_Tags/wp_list_authors
 * @since 1.2.0
 * @param array $args The argument array.
 * @return null|string The output, if echo is set to false.
 */
function sd_list_authors($args = '') {
	global $wpdb;

	$defaults = array(
		'orderby' => 'name', 'order' => 'ASC', 'number' => '',
		'optioncount' => false, 'exclude_admin' => true,
		'show_fullname' => false, 'hide_empty' => true,
		'feed' => '', 'feed_image' => '', 'feed_type' => '', 'echo' => true,
		'style' => 'list', 'html' => true, 'current_author_class' => 'current-author'
	);

	$args = wp_parse_args( $args, $defaults );
	extract( $args, EXTR_SKIP );

	$return = '';

	$query_args = wp_array_slice_assoc( $args, array( 'orderby', 'order', 'number' ) );
	$query_args['fields'] = 'ids';
	$authors = get_users( $query_args );

	$current_author_id = ( $current_author_class && is_author() ) ? get_user_by('slug', get_query_var('author_name'))->ID : 0;

	$author_count = array();
	foreach ( (array) $wpdb->get_results("SELECT DISTINCT post_author, COUNT(ID) AS count FROM $wpdb->posts WHERE post_type = 'post' AND " . get_private_posts_cap_sql( 'post' ) . " GROUP BY post_author") as $row )
		$author_count[$row->post_author] = $row->count;

	foreach ( $authors as $author_id ) {
		$author = get_userdata( $author_id );

		if ( $exclude_admin && 'admin' == $author->display_name )
			continue;

		$posts = isset( $author_count[$author->ID] ) ? $author_count[$author->ID] : 0;

		if ( !$posts && $hide_empty )
			continue;

		$link = '';

		if ( $show_fullname && $author->first_name && $author->last_name )
			$name = "$author->first_name $author->last_name";
		else
			$name = $author->display_name;

		if ( !$html ) {
			$return .= $name . ', ';

			continue; // No need to go further to process HTML.
		}

		if ( 'list' == $style ) {
			// add a class if appropriate
			if ( $author_id == $current_author_id )
				$return .= '<li class="' . $current_author_class . '">';
			else
				$return .= '<li>';
		}

		$link = '<a href="' . get_author_posts_url( $author->ID, $author->user_nicename ) . '" title="' . esc_attr( sprintf(__("Posts by %s"), $author->display_name) ) . '">' . $name . '</a>';

		if ( !empty( $feed_image ) || !empty( $feed ) ) {
			$link .= ' ';
			if ( empty( $feed_image ) ) {
				$link .= '(';
			}

			$link .= '<a href="' . get_author_feed_link( $author->ID ) . '"';

			$alt = $title = '';
			if ( !empty( $feed ) ) {
				$title = ' title="' . esc_attr( $feed ) . '"';
				$alt = ' alt="' . esc_attr( $feed ) . '"';
				$name = $feed;
				$link .= $title;
			}

			$link .= '>';

			if ( !empty( $feed_image ) )
				$link .= '<img src="' . esc_url( $feed_image ) . '" style="border: none;"' . $alt . $title . ' />';
			else
				$link .= $name;

			$link .= '</a>';

			if ( empty( $feed_image ) )
				$link .= ')';
		}

		if ( $optioncount )
			$link .= ' ('. $posts . ')';

		$return .= $link;
		$return .= ( 'list' == $style ) ? '</li>' : ', ';
	}

	$return = rtrim($return, ', ');

	if ( !$echo )
		return $return;

	echo $return;
}

Thanks!