I don't know of any way to download the Kindle books in bulk.
I have a K3 Kindle Keyboard, and I keep only a few books on it. I use
Kindle for PC software to organize my 1,700+ ebooks into collections. Other than some .mobi books, which I store on my PC, I keep all Amazon ebooks archived. Since the archived books can be put into collections using K4PC, I decided not to download them to the computer.
I understand that some people want to store the ebooks on their computer for backup purposes (or because they strip the DRM), but the method I'm using is working great for me.