WordPress: Related Posts based on category of current post

Related posts

<!-- This code is based on an old post in the WordPress forums: http://wordpress.org/support/topic/passing-current-single_tag_title-as-variable-into-new-wp_query#post-1001978 -->

<div class="related-entries">
  <div class="block">
    <ul>
      <?php
        //for use in the loop, list 5 post titles related to first tag on current post
        $cats = get_the_category($post->ID);
        if ($cats) {
        echo '<h3>Related Posts</h3>';
        $first_cat = $cats[0]->term_id;
        $args=array(
        'category__in' => array($first_cat),
        'post__not_in' => array($post->ID),
        'posts_per_page'=>5,
        'caller_get_posts'=>1
        );
        $my_query = new WP_Query($args);
        if( $my_query->have_posts() ) {
        while ($my_query->have_posts()) : $my_query->the_post(); ?>
        <li><a href="<?php the_permalink() ?>" rel="bookmark" title="Permanent Link to <?php the_title_attribute(); ?>"><?php the_title(); ?></a></li>

        <?php
        endwhile;
        }
        wp_reset_query();
        }
      ?>
    </ul>
  </div>
</div>

Thank you so much :)