For a few years now, Marvel Comics has been offering a digital subscription service called Marvel Digital Comics Unlimited, but today, they launched a much-higher-profile app for iOS devices and trimmed the name to Marvel Unlimited. (They promise an Android app will come "soon.") This is a big deal, because most people don't read on their desktops, or even their laptops. They read on their phones and tablets, and they're much more likely to read the comics on their mobile devices if they're readily available through an app.
The Next Web explains how it all works, but basically: For ten bucks a month or $60 a year, you get access to 13,000 digitized comics. You can only save six of those comics at a time to your device for offline reading. And Marvel makes a squishy promise that comics published this week might be added to the app in six months or so.
TNW says—and I agree—that Marvel Unlimited isn't really worth it yet. The reason I believe it's not worth it is that Marvel has a terrible track record producing trade paperback collections of their monthly comics. Their paperbacks come out too late to capitalize on a monthly book's buzz, and then they pop out of and back into print at weird times. With all the nerd internet buzz about Guardians of the Galaxy, for example, most of the relevent trade paperbacks aren't available right now. I simply don't trust Marvel to provide their new comics on a timely basis. Maybe one day, if comics stores go away, Marvel will operate on a digital-subscription-only model. I think they'd be able to get enough people to sign up for a $5-a-month subscription to fund the creation of new comics. But I think that day, if it does happen, is still a long way off.