WebSphere Application Server for z/OS Version 6.1: Moving an App to WebSphere z/OS

Over the last several years, many applications have been moved from WebSphere running on a distributed platform (Windows, UNIX, Linux) to WebSphere Application Server on z/OS. Most move up to z/OS without any issues. However, there are things that can cause the move to z/OS to be less than successful. They're not related directly to z/OS, but rather things that are frequently overlooked in the planning leading up to the move.