From http://wordpress.org/support/topic/using-meta-query-to-find-value-in-custom-field-array

new_gist_file

$posts = get_posts(array(
		'numberposts' => -1,
		'post_type' => 'link',
		'meta_query' => array(
			array(
				'key' => 'related_to',
				'value' => get_the_ID(),
				'compare' => 'LIKE'
			)
		)
	));