If you buy a paper notebook, it's yours to do whatever you want with. Sign up for a note-taking app, on the other hand, and you might face a totally different reality.

Evernote gave users new occasion to ponder that fact Tuesday, when it unveiled a new pricing structure that locks "free" users out of using the service on more than two devices. If you used Evernote on your Windows machine at work, Mac at home and smartphone in between, tough cookies: It's time to cough up some cash for Evernote Plus, which now costs $3.99 a month or a discounted $34.99 annually.

Techcrunch makes an interesting justification for the change in its post on the subject (emphasis ours):

The increased pricing may cause some short term frustration and a few people jumping ship, but as many of us have found, a service that works for us and into which we’ve poured years of data is generally worth keeping around, even if it increases in price by a few bucks. If Google had offered us the chance to pay $30 per year to keep Reader alive, you better believe they would have had a few takers!

Sure, Evernote's a convenient service that offers plenty of utility, even in its pared-down free version. The company is, of course, within its rights to charge a subscription fee -- and anyway, it's offering a grace period for people who rely on the more robust version of the free plan.

But let's be clear about what happened here: A productivity app that many people rely on fundamentally shifted its business model Tuesday, perhaps transforming into a very different product than the one you signed up for.

Imagine if, say, Google decided you could only have Gmail on one device at a time without paying a monthly fee. What if Facebook did the same thing? Evernote isn't in the same league, sure, but it's consistently ranked as the top productivity app on both Android and iOS -- tons of people use it. And like Facebook and Gmail, Evernote is built to house personal information and data you likely couldn't live without.

Evernote/iOS App Store A promotional image for Evernote says a lot about why it's so important to users.

This isn't really about Evernote in particular. It's about how we all use services today without really owning anything. Downloading an app and paying a subscription fee doesn't entitle you to much, ultimately. Evernote, like so many apps we love, is really just granting you a license to use its service when you sign up for an account.

This is a model that can end in tragedy, as it did when the beloved app Mailbox shut down late last year, forcing its users to find alternatives. And don't think my gut doesn't frost over when I consider I've probably dumped a few thousand dollars into "licenses to read" books on ComiXology, a service that could, unlike my bookshelf, theoretically dissolve from existence at some arbitrary point in the future.

What's to be done? Months ago, on the occasion of a WhatsApp shutdown in Brazil, cybersecurity expert Bruce Schneier called for legal protections.

"It is perfectly legal for Google to turn off your email address no matter how much it hurts your job, career, anything," Schneier said at the time. "We need to start having these discussions about when these systems permeate society to a degree that they become essential to living a full life. What are the rules these companies follow?”

We shouldn't panic over this Evernote shift. But should we worry a little bit more about what it represents?

Maybe so.