It sounds like an interesting idea for auto-saving article text or similar longer submissions, which are sometimes lost if you accidentally quit the browser or something else goes wrong.

Imagine if you're replying a long thoughtful reply to this post and you lose because you close the window, or your browser crashed. Load the page again and it'll be there.

We use this for Teambox, where users type long long descriptions for some things.

Any time you have a textarea element on your page.

Imagine you're writing a long response to a blog, and just as you are about to hit Submit, the page crashes. Now you can reload the page and your text will still be there!