I created a second free account to test the sharing feature before pushing in onto others (co-workers, wife, etc.). I have been able to share a project. Each person can add tasks. each person can reorder the tasks. The changes are made to both user's ordering. However, if the task is moved to another project by either user, it is removed from the other user. For projects I share with employees, I do not want them to be able to 'delete' the task simply by moving the task (accidentally or purposefully) to a different project in their system.