Since I have started at my new job we have been looking into several different PHP frameworks to use for the new development. We pondered doing a custom framework for the site but in the end we opted to go with CodeIgniter. I have to say that overall CodeIgniter is a really nice framework. It saves us a lot of time and code when we want to do simplistic things. The best part about CodeIgniter is that it is based on the MVC design pattern.
He gives an example of one way he's using the framework a Controller that loads in a custom library and uses it (to send an email). There's also a bit on how his application is set up - directory structure, using mod_rewrite, and even some issues that he's come across so far.