Facebook's "Subscribe" button, which lets you add someone's public updates to your news feed without friending them, is now available for external sites. People who have opted into the service can generate an embeddable button in either XFBML or iframe. Subscribing works similarly to liking a Facebook page, but it's intended for people who aren't public figures or don't want to maintain a separate account for fans. Instead of liking an entire news site and seeing updates from its page, for example, you can subscribe to a single writer's profile.
Subscriptions have been available for a few months, but this move makes the tool a more direct complement to the "Like" button and puts it in competition with Twitter. Facebook's system does have a couple of features that Twitter doesn't — you can select how many updates to receive, and subscribing to someone adds a message to your stream, letting friends subscribe directly from the news feed. Facebook hopes this will increase "viral distribution," a phrase we would really like to see limited to CDC alerts. Want to know where to subscribe? Check out the examples page.