Kohana is a lightweight PHP5 framework using the Model-View-Controller (MVC) pattern that's getting a lot of attention right now. It's ideal for use in smaller projects where the requirements and robustness of Symfony aren't required.
We have extensive experience of building mid-size and large custom CMS sites using Kohana, and during 2008 we provided a consulting lead developer for Kohana-driven projects to another web agency. With the exception of one site, all Kohana websites we have built are white-label and we regret we cannot illustrate them on this website.
We've also integrated Kohana into MODx CMS for an agency, so it could be used transparently in MODx modules.
We maintain two Kohana modules: one which integrates Doctrine ORM and another to provide code completion for PDT/Zend Studio.