The word “subscribe” is about to enter your daily vernacular with the addition of a new feature on Facebook that will allow users to better personalize their online experience.

Facebook has unveiled – in an attempt to curb the growth and keep up with features of Twitter, Google+ and others like it – a feature called “Subscribe,” which will allow Facebook users to, well, subscribe to the news of others. You’ll be able to begin hand-picking the content you want to view on your wall, thus fine-tuning the Facebook experience to your liking instead of having to see the somewhat random mess of updates from an array of people.

Subscribe is completely optional; if you don’t use it, Facebook will continue to run as it always does.

But for those who choose to use Subscribe, the benefits could be many. Like Twitter, instead of “friending” a celebrity or someone you’re really not friends with but are otherwise interested in, Subscribing will let you simply follow their updates (provided the person allows subscribers) without getting all their personal details. Subscribe means that popular or up-and-coming performers, writers, singers or comedians will see their stars shine a bit brighter. Self-proclaimed social media gurus will begin to measure their self-worth on the number of Subscribers they have. And you may find yourself with people you truly don’t know who are interested in what you have to share.

Subscribing may be the answer to keeping people on Facebook while tightening the experience to meet the demands of what people are looking for in today’s social networks: greater control, a more personalized experience, and a reason to stay at Facebook instead of another service: the people.

Facebook, unlike the rash of other services available, already has the critical mass. Yet if you take the pulse of savvy web users and even everyday Facebook users, you’ll hear stories of Facebook fatigue, the desire for more control over content, the need for privacy, or simply that they’ve done everything they can do on the site and are moving on. And while it is still growing, that growth is perhaps slowing (even dropping by 6 million users in May, Inside Facebook reports). It’s no death knell, but it could be telling.

For these reasons, we’re seeing more niche, focused communities pop up on Twitter, Tumblr, Instagram, Path and other platforms. They are more private, and the people on them more difficult to find.

This “privitization” of social networks is a trend we’ve been watching closely. And Facebook is about to board this train in a big way.

Not all of this is new, revolutionary or mind-blowing. But Facebook Subscribe is a bit of a mind-blower when you apply what this is and does to the masses of the social network, the paradigms in play in digital media, and the ever-increasing complexity of the modern identity.

Does it mean everyone will use and understand Subscribing right out of the gate? No, but its very existence is a product of some other trends and thoughts. For months (which is how we count technology time) people have been organizing their lives into separate places: Twitter for public thoughts, Tumblr as an extension of that community or to share personal interests with others, photo-sharing apps like Path or Instagram to share slice-of-life pictures and video.

Up until now, Facebook wasn’t really adequate in separating content as well as simple privacy. But with Subscribing, now even the non-savvy can start stratifying in new ways. People will share more, and less. Lives will take new shapes to certain people. And therefore, so will identities.

The layers of social soil just got more interesting for your garden.