In general this really works great, it can be difficult to set up given the amount of options it has. Also there are problems with captcha plugins, but that isn't really this plugin's fault.
One thing that is quite annoying which I would recommend you to remove is the pop-up in the admin section. Being a developer myself I understand that you need to expose your services etc. but that thing is a real PITA. Many don't really tolerate that kind of stuff and IMHO this can rather help you to reduce conversions instead of increase them.
Anyhow, thanks for a great plugin :)