Index: wp-includes/author-template.php
===================================================================
--- wp-includes/author-template.php	(revision 15468)
+++ wp-includes/author-template.php	(working copy)
@@ -368,4 +368,40 @@
 	echo $return;
 }
 
+/**
+ * Returns true if there is more than one user with a published post
+ */
+function is_multi_author() {
+	global $wpdb;
+
+	$users = get_users_of_blog();
+	$author_ids = array();
+	$authors = '';
+	foreach ( (array) $users as $user )
+		$author_ids[] = $user->user_id;
+	if ( count($author_ids) > 0  ) {
+		$author_ids = implode(',', $author_ids );
+		$authors = $wpdb->get_results( "SELECT ID, user_nicename from $wpdb->users WHERE ID IN($author_ids) " . "ORDER BY display_name" );
+	} else {
+		$authors = array();
+	}
+
+	$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;
+
+	$multiple_authors = '';	
+	foreach ( (array) $authors as $author ) {
+		$posts = (isset($author_count[$author->ID])) ? $author_count[$author->ID] : 0;
+		
+		if ( $posts != 0 )
+			$multiple_authors = $multiple_authors + 1;
+	}
+	
+	if ( $multiple_authors > 1 )
+		return true;
+	
+	return false;
+}
+
 ?>