slow queries coming from related posts plugin

gistfile1.sql

SELECT
  		target.post_id, sum(target.weight * log(34759 / least(34759, freqs.freq))) as score
		FROM
			wp_1_wp_rp_tags as target,
			(SELECT label, count(1) as freq FROM wp_1_wp_rp_tags
				WHERE label IN ('P_audacity', 'P_runtime', 'P_soundflower', 'C_articles', 'C_tutorials', 'A_max', 'A_mac', 'A_softwar', 'A_audio', 'A_sketch', 'A_os', 'A_free', 'A_download', 'A_aa', 'A_patch', 'A_project', 'A_instal', 'A_machin', 'A_product', 'A_sound')
				GROUP BY label
			) as freqs
		WHERE
			target.post_id NOT IN ('17274') AND
			target.label=freqs.label AND
			target.label IN ('P_audacity', 'P_runtime', 'P_soundflower', 'C_articles', 'C_tutorials', 'A_max', 'A_mac', 'A_softwar', 'A_audio', 'A_sketch', 'A_os', 'A_free', 'A_download', 'A_aa', 'A_patch', 'A_project', 'A_instal', 'A_machin', 'A_product', 'A_sound') AND
				target.post_id NOT IN (
					SELECT post_id FROM wp_1_wp_rp_tags
					WHERE label IN ('C_blog', 'C_company', 'C_newsletter', 'C_press releases', 'C_review', 'C_Uncategorized')
				)
		GROUP BY target.post_id
		ORDER BY score desc
		LIMIT 6;