for what it's worth - I've combined the use of a Windows batch file that I keep on my Kindle along with dropbox to make a very easy to use and quick and painless backup of all of the files on my Kindle. When I plug my Kindle in to my PC (by USB) all I have to do is double-click my batch file, and it automatically copies any and all new or changed files to my dropbox folder on my PC. It works great - I can post the batch file up here if anyone is interested.
(oh, and the now obligatory dropbox link - sorry , had to do it...
http://www.dropbox.com/referrals/NTEwODMzMjIzOQ
