You can set up automatic notifications via Growl, which has options to send email and SMS alerts (the latter via a paid service, I believe).
http://growl.info to download.
The notification calendar feature writes a calendar full of 0 minute appointments the configured interval before the due date of actions with due dates in the next 14 days, and updates it every time the iPhone application does a sync. In the future, the desktop application will also update this calendar, but for now, only syncing the iPhone app will update it. If you've subscribed your iPhone's calendar app to this calendar, you'll get popup notifications of those due items even if you are in another application or don't have internet connectivity. It isn't intended to be used as a calendar of what you need to work on and when, just a workaround for a hole in the lineup of services Apple offers to developers.
If you search the forums a bit, there's an Applescript posted by Brian that sounds like it might do a bit of what you want. Personally, I like to get my "due" stuff out of the way a bit earlier than the length of time it will take to do prior to the deadline, because no matter the schedule I set, I rarely get to keep it!