Nate Hoffelder at the Digital Reader reports that Barnes & Noble is dropping its Nook e-reading service in the United Kingdom. If you own a Nook e-reader, that could turn out to be a real problem. For one thing, you might not be able to access your books anymore. For another thing...
...if you should have to reset a Nook UK device in June, you won't be able to reauthorize it to the same account. And if someone gives you a Nook UK device in June or later, you won't be able to log in using your current credentials. And since B&N requires that a Nook device be authorized before you can use it, that is a problem.
Not to be a dick, but you literally never have to worry about this kind of thing with physical books.