Not effective for semi-automated spam

Didn’t find it effective at all, in fact my observation was that spam increased significantly after I disabled other anti-spam plugins (except Akismet) and enabled this one. I think the root of the problem lies here (referring to another product). It appears I am having to deal with this type of “semi-automated” spam:

I think our definitions of “automated” spam differ quite a bit. It’s true that a good portion of automated spam comes in the form of direct POSTs to a blog; your plugin will definitely block these. But there are several forms of automated spam that come in the form of scripted bots that load the page in a browser (headless or otherwise) and actually fill out the form to trigger the postback. There is little that distinguish these from regular comments besides the time it takes to complete the form, and the often gibberish-level content submitted. These spam comments are also “automated” but will make it past your plugin. Granted they are much more rare, but have proven to be an issue on many sites I’ve worked with.

http://eamann.com/tech/plugin-review-spam-free-wordpress/