This report from Gear Diary paints a unpleasant picture for Amazon’s download policy for Kindle. It seems that there’s a limit to how many times you can download a book, but that limit isn’t posted anywhere.
Here’s an excerpt of the article, but it’s worth reading the whole thing.
The customer rep asked me to send every one of the books in my Amazon library to my iPhone. Most of them gave the message that they were sent but a number of them returned the message “Cannot be sent to selected device”.
“Oh that’s the problem,” he said “if some of the books will download and the others won’t it means that you’ve reached the maximum number of times you can download the book.”
I asked him what that meant since the books I needed to download weren’t currently on any device because I had wiped those devices clean and simply wanted to reinstall. He proceeded to tell me that there is always a limit to the number of times you can download a given book. Sometimes, he said, it’s five or six times but at other times it may only be once or twice. And, here’s the kicker folks, once you reach the cap you need to repurchase the book if you want to download it again.