What do you like best?
Zend Studio is created by the folks who make Zend, so what better tool is there to use?! It sits on top of Eclipse and offers several code repository integrations and frameworks that snap in. As you're developing, the built in code completion is responsive, and the built-in documentation is spot on. It's flexible enough for all of your PHP development needs
What do you dislike?
As with any piece of software, there are some quirks. We often times use SVN for some of our code repositories, and way the software caches credentials isn't optimal. On particularly large repo imports, it can take an extended period of time to add the project. Better real-time status updates for these processes would be helpful.
What business problems are you solving with the product? What benefits have you realized?
We do custom PHP development in our environment, and this tool solves the issue of an IDE that's designed and tuned specifically for PHP. My developers like it, I've been using it for well over 5 years, and it's an actively maintained and smartly improved piece of software.