At out company we currently use JIRA within a project whose only deliverables are text documents. In this project we use JIRA as a task list for the individual project members. We create issues of type Task and assign them to the person in charge. Usually we want to associate a "due date" with the task.
At first we solved this by adding a custom field "Due Date". This was not quite satisfactory as we can't filter using this custom field. Instead we now schedule the tasks with specific project versions. The problem with this approach, however, is that a future version can't have a scheduled release date (which would be the due date for the issues fixed by that version).
I think it would be reasonable to have a way to specify a scheduled release date for a project's unreleased versions.