While we're on the topic, when was the last time you backed up your ebook collection? You can't rely on the ebookstore being there for you to download again. Fictionwise, Sony, and Amazon have all pulled ebooks at one time or another, and I know of at least 1 ebookstore that closed without warning.
Unfortunately, a lot of ebooks are encumbered by DRM, and that DRM will screw up the backup process. Now might be a good time to start learning about how to strip DRM so you can protect your purchases.