the wheel -reinvented

<?php
$this_post_id = $post->ID;
$categs = get_the_category($post->ID);
foreach($categs as $cate) { $post_cats[] = $cate->term_id; }
$args = array(
'posts_per_page' => -1,
'category__in' => $post_cats
);
$this_query = new WP_query( $args );
if($this_query->have_posts()) :
while($this_query->have_posts()) :
$this_query->the_post();
?>
<h3<?php if($post->ID == $this_post_id) echo ' class="active"'; ?>><a href="<?php the_permalink(); ?>" title="link to <?php the_title(); ?>"><?php the_title(); ?></a></h3>
<?php the_excerpt();
endwhile;
endif;
wp_reset_query();
?>