On the Zend Developer Zone there's a new article that looks to answer the question in its title - "Why should I care what server my application is running on?" (by Eddo Rotman)

Imagine this - you develop an application on your machine and then, when you come to deploy it to the production server, all of a sudden, you encounter various errors and failures. Or maybe, when you decide to switch your hosting provider, your application stops behaving the way it should. How about this -... one day, out of the blue (well, out of your IT manager's whim) your application just misbehaves. Sounds familiar?

Times like can never be completely avoided (yes, there'll always be bugs) but you can take some steps to help prevent most of the major failing points. He points out some of the key configuration directives to watch out for, differences in some functions' responses based on the OS, and the differences in character sets between a unix-based and Windows based environment (like rn versus just n).