On the MaltBlue.com site today there's a new tutorial posted giving you some recommended practices on building an extendible application with the Zend Framework.

Whether you have a big or small budget are time rich or poor, there’s always the pressure to build applications with the future in mind. [...] So amongst the multitude of other advice you’ll receive throughout your life, building applications that are readily extensible and extendable – in a simple, clean and cost-efficient manner – is essential to keeping input as low as possible, whilst maximising output, and accompanying client satisfaction (or boss satisfaction if you’re full-time employed).

He focuses on one aspect of Zend Framework that he's found that helps out the most in keeping his development flexible, resource plugins. These plugins (through use of the Strategy design pattern) can add immediate functionality to your application and be dropped in as needed. He shows how with a simple plugin that allows for simpler file handling for user uploads. The code for the various parts - interface, factory, plugin and resource - are all included.