In his latest post Brandon Savage suggests that every developer should do one thing before they start working with PHP frameworks - write their own.

So for those of you wanting to write your own frameworks, feel free. But don't even think about putting it in production until you've read this blog post. Lots of times new developers are shot down from writing their own frameworks by bosses or community members who insist that "NIH" (not invented here) has no place in their organization or language. [...] To me, that doesn't make a whole lot of sense.

He points to a comment from Elizabeth Smith that reinforces his ideas and supports the creation of a framework. Using it in production, however, is a whole different story. They both agree that writing your own framework is good for learning how it all works, but that you should stick with the larger frameworks for real development.