I just hacked up a little code snippet based on Matthew's Honeypot Wordpress plugin. It's basically just a Validator for a Zend Form element which is hidden from the user via CSS. Cause it's hidden, users won't see it, but spambots will, well, cause they are bots.

The code snippet is included in the post for your cut & pasting pleasure and makes using it as easy as a normal "addElement" call when building your form.