Robert Agcaoili on due dates:
For me, the obvious answer to putting priority on tasks that need to be completed “at my convenience” was to put soft due dates on them. For the unaware, soft due dates are arbitrary due dates you assign despite the fact that nothing disastrous would occur if you happened to miss that date.
I very strongly think that if a task is not absolutely due at a certain time and date, then you shouldn’t use a due date for that task.
That’s what flags are for, and Robert touches on this in his post.