I've gone ahead and added validation to our test project. If you take a look at the indexController you'll now see I've added an updateAction that uses a Zend Form component. The goal of the validation was to provide context sensitive validation on a model.
He's set up a system that allows you to add "validators" to the model to define how it should handle itself. A later call to "isValid" uses this context to see how it should be evaluated.