Part of the attraction of the Kindle, outside of other things I've posted about it, is the ability to share purchased books with up to 6 other devices. This isn't entirely perfect yet as the devices all have to be linked to the same purchase account (i.e., someone with a Kindle on my account can place orders using my credit card), but it's still pretty cool if that's not a concern for you.
Perhaps I missed it or just didn't look in the right place for it, but I couldn't figure out how to get access purchased content that was deleted and/or purchased content I wanted to put on another device from the Kindle -- that's because you can't. What you have to do is access yourmedialibrary on Amazon; this is where all of your digital purchases (e-books, music, movies, etc.) is stored. As it relates to the Kindle, from the yourmedialibrary dashboard, you can choose to resend a book to your Kindle via WhisperNet, send a purchased book to another Kindle on your account via WhisperNet, or download the e-book to load it via the USB cable (this must be the solution for purchasing books while traveling outside of the WhisperNet coverage area).