At first the plugin worked, as I could the notes in webpage, and I had low CPU usage, but then I changed "Automatic Expiration Time (Max Age)" to "30 minutes", then to "2 hours" and I have high CPU usage, but pages are still generated in /wp-content/cache, and I can't see the notes at bottom, when I access the website without being logged. I'm using Firefox as admin, and Chrome as a visitor (not logged). All other params are default.
By the way, the website is using CloudFlare + nginx + php5-fpm, so I don't know if this could impact your plugin because visitors may seem to come from the same IP.
My website is http://www.cnx-software.com.