I’ve created a Greasemonkey script (and a Firefox Add-on) that adds an unobtrusive AutoSave feature to WordPress 2.0.2 and probably all the other WordPress versions 2.x. Could be that it even works with previous WordPress versions.
I decided I need to write the script after I lost a half of a post two times in a row because I accidentally pressed the ‘Back’ button on my new ThinkPad keyboard. This annoyed me so much I went to check if there are AutoSave plugins available. When I didn’t find any (one had the page unavailable, the other possibility was upgrading to 2.2) I decided to write a GM script. It’s pretty easy and as I wrote it the functionality enhanced itself. It’s useful for me, it might also be useful for you.
More about the WordPress AutoSave script on its own page.