We were getting hit from numerous (15+) spam messages a day. We figured this was an acceptable number to just handle manually, but quickly grew tired of taking the time to moderate these comments, marking them as trash.
We tried various CAPTCHA plugins but none were very graceful. From difficult-to-read CAPTCHA strings to stark, unstyled "You have entered an invalid CAPTCHA" message, none of the CAPTCHA plugins we implemented really worked for us.
Then I found this plugin. It's so simple in its implementation that it's almost laughable. There's beauty in what it does, though. It's not overly complicated, it doesn't affect the aesthetic of the site AT ALL, and most importantly, it just works.
I've had this plugin installed for over a week and have not received a single spam comment. I give it five stars all day long.
Just as a test, I went and toggled the value that sends spam comments to the site administrator. No less than 30 minutes later, I had received a message that was spam. I've since toggled the value back to "false" - but it's sure nice to know the plugin is working. :)