Another anoying thing is when commenters do not make links to hyperlinks, as these are not linked and clickable afterwards. We have found a solution for these problem – just copy the following script to your functions.php-file and your comments will be sanitized:

add_filter('preprocess_comment','format_the_comment_html');
 
function format_the_comment_html($comment_data) {
	$comment_data['comment_content']=nl2br(makeClickableLinks($comment_data['comment_content']));
	return $comment_data;
}
 
function makeClickableLinks($text) {
	$text = eregi_replace('(((f|ht){1}tp://)[-a-zA-Z0-9@:%_\+.~#?&//=]+)','\\1', $text);
	$text = eregi_replace('([[:space:]()[{}])(www.[-a-zA-Z0-9@:%_\+.~#?&//=]+)','\\1\\2', $text);
	$text = eregi_replace('([_\.0-9a-z-]+@([0-9a-z][0-9a-z-]+\.)+[a-z]{2,3})','\\1', $text);
	return $text;
}