Thanks for the plugin. My use case is that I'd like to use recaptcha on business directory forms as well as wordpress forms (ie register).
What I've found is that, since business directory borrows code from wp-recaptcha plugin, it causes class/function collisions, fatal errors and erratic behaviour. However, I need to install a second wp-recaptcha plugin to protect my register page I think.
Is there any chance you could move your copies of the recaptcha classes to another namespace?