Back in the Fall of 2010, we needed a new PHP framework for our applications. Neither of our applications - Newscoop or Airtime - had anything that could really be called a framework, though our code was generally separated into Models, Views, and Controllers (MVC). But it wasn't pretty. We were in need of an established MVC framework to build on.
They tried out several different frameworks including Yii, CakePHP, Kohana, Symfony and, of course, the Zend Framework. They talk briefly about their evaluation process and some of the pros and cons they found along the way.
Overall, using Zend has helped us to create clean, structured code and for most cases has lowered our implementation time for new features. [...] Even though there are some things that could be better, the net benefit has been positive for us.