They make great gifts.
Not so ebooks or, at least, Kindle books: despite what this help page says, the damn “Give as a Gift” button is nowhere to be found.
A quick query to Customer Service elicited a courteous answer from a rep confirming that:
[...] presently it’s not possible to send kindle content as Gift to a number of email addresses.
However, I’ve forwarded your comments as a feedback to the Kindle Development team who will be glad to review your comments. They are always looking for ways to improve our service and may be able to make this feature available in future.