I know it is not good practice to assign due dates to tasks when using the GTD methodology. However, when serving multiple clients where there are many items attached to a specific due date, I find it better to assign the due dates in the task rather than put it on my calendar (which clutters my calendar far too much, especially on my Smart Phone). Also, when you assign due dates to Tasks in Outlook you can have them show up on your desktop client calendar at the bottom.
The negative to this method is that you may have many items that are past due that you wish to move to another date. My Google-Fu must have been busted, because I could not find out how to do this, so I resorted to manually changing each one.
Today, I finally figured it out! And being the nice guy I am, the fruits of my labor are now available to all. 🙂