I've got something put together now that resembles a draft. For each post you start to type stuff into, it will save your progress every 10 seconds.

Your progress will be saved until you submit your post, after which, your draft for that post will be purged.

Your draft will stay with each post, so you can potentially craft multiple drafts at a time. So, don't be surprised if you start seeing old, forgotten stuff in the comment box. It's there. Waiting. Forever.