About a year ago, Apple debuted in-app subscriptions on its App Store - now Google is following suit with the introduction of in-app subscription support on the Play Store. Developers can take advantage of this system very easily, by simply adding a subscription option to their apps with a price and billing period (subscriptions will show up for users in their Play Store under a new category). Google takes care of the rest - all subscriptions are auto-renewing, and can be managed by users through the Play Store interface.
Bigger developers can utilize an HTTP support API to hook in-app subscriptions into backend enterprise servers for validation and cancellation (read: DRM), as well as to make multi-platform subscriptions easier to manage. For example, buying a subscription to a publisher's entire suite of services on a variety of apps through a single in-app purchase could be accomplished without the need for messy logins - download another one of the publisher's apps that grants access to premium features through the subscription, and it just works.
One of the first developers taking advantage of the HTTP API will be GluMobile, in the form of an in-game currency subscription (disgusting, I know) that can be used across all of the company's titles, without the need for a 3rd-party login or account management service. Nifty.
To learn more about in-app subscriptions, check out this Android Developer Blog Post.