How many times have you been writing a comment and clicked on a link in the comment thread to reference something and lost your comment in the process? Loose a message because Chrome crashed for one reason or another? Accidentally hit the refresh button?
The Autosave for Basecamp plugin will automatically save your message in real time as your typing it using Chrome's HTML5 local storage technology. Hit the refresh page, write a message and come back to it later, close the browser - your message will still be there!