get_comment_replies() function for WordPress with a working example that returns a WordPress comment object for a given comment ID annotated with "reply_count" and "replies" properties.

test-get-comment-replies.php

<?php
/*
*  test-get-comment-replies.php
*
*  Returns a comment object for a given comment ID annotated with "reply_count" and "replies" properties:
*
*     reply_count: count of all replies including sum of child replies.
*     replies: array of child comment objects also annotated with "reply_count" and "replies" properties, recursively.
*
*  Examples:
*
*     // Get comment with nested replies for comment ID = 55
*     $comment_with_replies = get_comment_replies(55);
*
*     // Get all comments with nested replies for post ID = 17
*     $comment_with_replies = get_comment_replies(0,array('post_id'=>17));
*
*     // Get ALL comments with replies
*     $comment_with_replies = get_comment_replies('all');
*
*  In response to: http://lists.automattic.com/pipermail/wp-hackers/2010-September/035086.html
*
*  Save this example test file in the website root as /est-get-comment-replies.php and call it like so:
*
*   http://example.com/est-get-comment-replies.php?comment_id=123
*
*  By Mike Schinkel
*
*/
	header('Content-type:text/plain');
	include "wp-load.php";
	$args = array();
	if (isset($_GET['post_id']))
		$args['post_id'] = $_GET['post_id'];
	$replies = get_comment_replies($_GET['comment_id'],$args);
	print_r($replies);

function get_comment_replies($comment_id=0,$args=array()) {
	$args = wp_parse_args($args,array(
		'post_id'=>0,
		'orderby'=>'comment_parent',
		'order'=>'ASC',
	));
	extract($args);
	if (is_numeric($comment_id) && $comment_id>0 && !$post_id) {
		$comment = get_comment($comment_id);
		$post_id = $comment->comment_post_ID;
	}
	if (!$post_id && !is_numeric($comment_id) && $comment_id!='all') {
		wp_die('get_comment_replies() will not parse all comments unless explicitly requested.');
	}
	$comments = get_comments($args);
	$replies = array();
	foreach($comments as $comment) {
		$comment->reply_count = 0;
		$comment->replies = array();
		$replies[$comment->comment_ID] = $comment;
		if ($comment_id==$comment->comment_ID)
			$this_comment = $comment;
		if ($comment->comment_parent) {
			if (!isset($replies[$comment->comment_parent]->replies))
				$replies[$comment->comment_parent]->replies = array();
			$replies[$comment->comment_parent]->replies[$comment->comment_ID] = $comment;
		}
	}
	$children = array();
	$count = 0;
	if ($comment_id>0) {
		$this_comment->reply_count = _count_comment_replies($replies,$comment_id);
		$this_comment->replies = $replies[$comment_id]->replies;
		$replies = $this_comment;
	}
	return $replies;
}
function _count_comment_replies(&$replies,$comment_id) {
	$count = 0;
	if (count($replies[$comment_id]->replies)>0) {
		$count = count($replies[$comment_id]->replies);
		foreach($replies[$comment_id]->replies as $index => $reply) {
			$count += _count_comment_replies($replies,$reply->comment_ID);
		}
		$replies[$comment_id]->reply_count = $count;
	}
	return $count;
}