On my vBulletin forums there is a product that inserts a hidden input field on the registration page. The only way that this field would ever be populated is by spammer bots filling in every input on the page. It has done wonders to stopping spam. I would like this for xenForo. Basically, when you click to register the code checks to see if the hidden field is empty. If it is, the registration is allowed. If the field is not empty, registration is denied and the ip address, email and username of the spammer trying to register is sent to StopForumSpam database.