This is the best example I've seen. We've spent the last 20+ years training the public that ".com", ".net", etc equals "website". Now that anything could be a URL, it's going to be a lot more confusing for people.
The owners of (books|music|whatever).com are going to be happy because a good number of people are going to see "best.books" and end up thinking that means "best.books.com"