We are already receiving pings on this one and, thanks to our crack engineering staff, have updated IntelliGantt and the IntelliGantt Add In for Microsoft Project. Now IntelliGantt will publish the Finish dates of your tasks as Due Dates within Basecamp.
The value here is whenever you need to reschedule a project, you have the full power of a rich scheduling engine to automatically adjust the dates and the rich integration of IntelliGantt to automatically all the due dates within Basecamp.
We will keep the 'old way' of adding due dates to ToDo Items so that it will be easy for people to back out of it. Just go to Settings->More Settings and turn off the Append/Prepend due dates selections.
Going forward, all tasks will have their Due Dates in Basecamp populated because that's what IntelliGantt does-- help you schedule (and share) tasks.
We will have a screencast showing the integration on Monday, but you can try out this new IntelliGantt feature today if you'd like.