"Subscribe to this friend," or "Facebook subscribe" is a Facebook feature now in beta that would allow users to receive notifications whenever a certain person does anything on Facebook, including change their relationship status. Some are already calling this the "Facebook stalking" technique, which should open up the social networking site to the kind of harsh criticism they're probably getting used to.
Facebook is apparently testing a new subscription feature that would allow users to receive alerts any time a specific friend takes certain actions on the social network.
AllFacebook reports that it has noticed the new feature popping up on friends’ profiles. Facebook told the blog, “This feature is being tested with a small percent of users. It lets people subscribe to friends and pages to receive notifications whenever the person they’ve subscribed to updates their status or posts new content (photos, videos, links or notes).” [Mashable]
Since statistics show many men Facebook-stalk their exes, if the idea of being Facebook-stalked by an ex creeps you out, maybe you should consider unfriending them.