The great thing about the Zend Framework is that you can cherry-pick the classes you want to use and ramp up slowly to using the full framework. It has all the MVC goodness that the other players have if you want to go that far. I'm planning to start with the DB, Filter, Cache, and Auth classes and see how it goes.
With CakePHP or Symfony, it's all or nothing. But some people like it that way I suppose. Different strokes for different folks...