Intuitive control is the most important aspect of the system. GTD implements all modern features including drag&drop. This way user can change the order of the sections only by dragging them by mouse. The order is stored in the database on the backround so desktop stays in the same shape even next time user login.
In the same way you can move each activity in the section and by this prioritize item. You can move activities between sections as well. All changes are again stored in the database.