Location: I'm the uber Spaminator !
Yes, it's possible.
For that, you will need to identify the user though.
Either via a cookie (weak, can be altered or dropped easily) or via a login form.
Then, each time the focus is lost on the textarea, use a xmlHttpRequest (ajax) object to send to the db which text-area it is, it's content, and the id of the user.
Next time he comes back to that page, simply check the db for existing content and pre-fill the textarea.
Only a biker knows why a dog sticks his head out the window.