I give Zend_Form a couple of tries. I recognize it is a really cool component. However, i think it kind of violate the layer separation law. What if a designer wants to decorate the form? He must open up the PHP file and learn how Zend_Form work?
In spite of this, I cannot resist the temptation of using this component. The benefit is it can save a lot of time. With Zend_validator and Zend_Filter, Zend_Form can finish most of form processing job for you. You, as a developer, probably just need to add some extra own validators and that is it!