This plugin will backup your posts when your connection goes down in the middle of you editing a post.
Let's say you're on the train and you're writing on a post you started at home. The train enters a no-signal area just when you're about to press "Publish".
The browser takes you to a "Page not found" message and that's it. Pressing back sometimes doesn't bring back all the work.
This plugin takes care of that situation, and a lot of others. Once you're in the editor, you can forget about your connection. Just write. Hit publish when done. You'll be notified next time you're on the blog if you still want to publish.
Developed as part of Google Summer of Code 2011.