Now this would be nice, saving as a draft that is. Many times I've had to stop mid-way in a comment to go and research something, it would be nice to save the draft.
On a related note, a couple of times I've hit "Back to Discussions" instead of "Add your comments" but I don't think Auto Save is very easily doable in a web browser.
There was an old clipboard extension (0.9.3) that you could use to save snippets of text, then pop them back into a comment form. It needs some fixing up to work with Vanilla 1, if anyone wants to volunteer.
I don't really like the idea of a drafts folder. I seem to periodically draft an email which was meant to be sent. Wind up annually cleaning out a drafts folder with 5-6 messages in it.
I would imagine a better autosave should save the comment form and auto-fill the form with that information whenever that user next encounters such a form, rather than force the user to select which draft to pull from.