I have been working on, and just went live with, a long and complex form that is being submitted by the public.
I've already started to hear some grumblings about the save for draft feature.
If they save the draft, in order to save their progress on their from, they are logged out and have to log back in via email. In at least one case the user said they didn't receive their email right away, leaving them with the option to either start over again, or wait for the email to arrive to finish the original form.
We need the ability for the user to "save progress" without being logged out.