This blog post offers a cautionary story on how Amazon can wipe out your entire account:

As a long-term writer about technology, DRM, privacy and user rights, this Amazon example shows the very worst of DRM. If the retailer, in this case Amazon, thinks you’re a crook, they will throw you out and take away everything that you bought. And if you disagree, you’re totally outlawed. Not only is your account closed, all your books that you paid for are gone. With DRM, you don’t buy and own books, you merely rent them for as long as the retailer finds it convenient.

One reason I still prefer to own physical books versus e-books.