Freshy 2 gravatars fix for 2.5 and 2.6:

Edit comments.php inside theme folder and replace:

<?php // gravatars
if (function_exists('get_avatar')) {
if ('' == $comment->comment_type) {
echo '<img class="avatar" src="';
get_avatar($comment->comment_author_email);
echo '" alt="'.$comment->comment_author.'" width="40" height="40" />';
} elseif ( ('trackback' == $comment->comment_type) || ('pingback' == $comment->comment_type) ) {
echo '<img class="avatar" src="';
get_avatar($comment->comment_author_url);
echo '" alt="'.$comment->comment_author.'" width="40" height="40" />';
}
} else {
//echo '<img class="avatar" src="'.get_bloginfo('stylesheet_directory').'/images/default_avatar.png" alt="'.$comment->comment_author.'" width="40" height="40" />';
}
?>

with this:

<?php // gravatars
echo get_avatar($comment,$gravatar_size,'');
?>