One of the Drupal sites we maintain had recently started slowing down considerably in spite of the site mostly being static and in spite of boost set up on the server. On examination of the site we found that two things were happening on the site. One was that the site was being crawled indiscriminately by rogue crawlers. This we solved using the DDOS deflate script and setting DDOS deflate to run every 10 seconds. The second problem was that there were some bots which were continuously sending POST requests to /comment/cid/reply pages. For this we had to come up with a workaround.