I have an external USB hard disk that I use to store all my documents on. I move it between my laptop and my desktop PC so that when I’m out with my laptop I still have access to all my files. And when I get back I don’t have any synchronisation issues.
However, I don’t seem to be able to tell Windows Live Writer where to save my drafts (e.g. A blog folder on my external HDD) so it all ends up in My Documents.
I don’t suppose it will be too difficult to take a USB stick and copy the posts from one to the other, but I’d rather just plug the HDD in and go.