There was once talk about locally saving during your post time just in case your internet connection died half way through. Something that assumes a connection and saves as a draft every now and then never came up, but I think it'd be kinda neat.

You would either need a iframe/object or the famous xmlhttprequest.
I think object would be better as it would be easier to customize.
Just have a mini write form, and you just give it the current data and make it submit itself each 2minutes or so.
Should work as long as the user doesn't change the post title or post id string thing....

I think doing it this way would be best because i would get pissed off if each 2 minutes my page refreshes itself.

Well if you could figure out how Gmail does it it would be great as the page doesn't have to refresh.

Gmail does it via one of the ways i said above.