A lot of people have been asking for some comparison articles for some of the popular frameworks. Here I found a nice comparison between Zend framework and CakePHP framework from Douglas Brown.
ZF offers a simple component library to provide 80 percent of the functionality mostly needed by developers. The rest of the 20 percent can be altered as per your requirements of the business. This can be done since it has a flexible architecture and you do not need any configuration file to get started with. Due to this, training costs are lessened and the product reaches the market sooner.
CakePHP is a rapid development framework for PHP that offers a flexible architecture for development, maintenance and deployment of applications. It uses the usual design patterns like MVC and ORM within the convention over configuration paradigm that helps lower development expenses and does not need the developers to write a lot of code.
Just like ZF, CakePHP does not require configuration. It is very simple to use. The company has a user friendly community called #cakephp on IRC that helps new users to begin. It is distributed under the MIT License and promises Best Practices like security, authentication and session handling. It has an object-oriented approach to keep you at ease.
Overall, both these frameworks are good to use as per your requirements. CakePHP is suitable for developers new to MVC and those who require stricter conventions. ZF is a choice for those who need better control over the application design and built-in support for renowned Web services. Both the frameworks are developing fast and the choice is entirely yours.
Some of the people noted that CakePHP has poor documentation. The Zend Framework definitely has better documentation. So if you were just getting started using an MVC Framework, ZF would be a good place to start.