This is part of Farhad Manjoo’s continuing series on the future of innovation. Read the series introduction, Manjoo’s stories on the future of mobile gadgets, the future of the Internet, and the future of home entertainment, and readers’ predictions about mobile devices and the future of the web.

On Wednesday, to no one’s surprise, Google launched yet another effort to take on Facebook. The new service is called +1, and it works just like the Facebook Like buttons you now see all over the Web (including on this page). When you come across a link in Google’s search results that you want to share with your friends, you can click the +1 button. When your friends do a similar search, they’ll see your recommendation. For now, the +1 button appears only on Google’s search pages, but the company will soon allow publishers to place them on other sites, too. This might sound superfluous—don’t we already have enough ways to tell people what we like online? With Facebook, Twitter, Reddit, the nearly departed Digg, and good old email, it sometimes seems like the Internet is overflowing with suggestions. How much more recommending do Web companies think we can stand? Will this ever stop?

Nope. Not soon anyway. Over the last few weeks I’ve been writing a series on the future of technology. In this last piece, I’m looking at one of the most volatile, exciting, and unpredictable parts of the Web—social networking. The proliferation of social sites hit its peak a few years ago, when every start-up and Web giant seemed be releasing its own network. Now the fight seems relatively settled: Facebook, with its more than 600 million “active users,” has trounced everyone else, and with the Like button and the rest of its plugins, it has managed to co-opt the rest of the Web, too.

Despite this success, I often hear from readers who suggest that Facebook might be a fad. Someday soon something new will come along, they argue, and we’ll all switch over to that. The larger complaint is that social networking isn’t an important tech trend—that it’s something we’ll get over, and that what really determines the future of tech are the chips, algorithms, and other stuff computer scientists work on. These comments, it seems to me, reflect a deep concern about what all our friending, Liking, and sharing amount to. Readers often complain that Facebook in particular, and social networking in general, detracts from real-life relationships. We’re worried not just that it’s going to change the Web, but our offline lives as well.

Let me go out on a limb and declare that Facebook isn’t going to go away anytime soon. The site is more entrenched than just about any other technology we use. It’s easy to go to a new search engine—just type Bing instead of Google—and there’s nothing stopping you from switching your brand of computer or cellphone. You can’t switch over to a new social network, though, unless your friends do so as well. Sure, this could happen—fashions change, of course, and the inherent stickiness of social networks didn’t save all the ones that came before Facebook. But Facebook seems to have hit a critical mass. Not only does it have a huge number of users (more than any previous social network), but its audience is spread across every demographic (which wasn’t true of MySpace), and they’re ferociously committed to the site (nearly half log in every day). It also shows no signs of slowing its growth—and the bigger Facebook gets, the harder it becomes to switch to a new platform. If a storm of criticism surrounding its privacy practices and its frequent, confusing redesigns haven’t done anything to stem its growth (and those controversies haven’t), I’m not sure what could push Facebook off the main stage in the near term.

The big question for the future of social networking isn’t whether Facebook will be the largest and most influential site five years from now. It’s whether it will be the only one. Will Facebook be the exclusive catalog of our interests and relationships, or will it coexist with several others?

This is what I meant when I said that the future of social networking was unpredictable. There are huge swaths of the Web that aren’t under Facebook’s sway: When you email someone a link, share photos on Flickr, or review a restaurant on Yelp, you’re engaging in “social” activity outside of Facebook’s purview. Sources at Google have told me that even though the search company doesn’t have a successful social network of its own (Orkut doesn’t count), Google believes it can build a realistic picture of your social life by mining all this other activity. That seems to be what it’s doing now: With your permission, Google indexes some or all of your activity on Twitter, Flickr, and Quora. It also keeps track of social networks you’re building in Google’s own products (people in your Gmail chat list, your Google Contacts, or people you follow on Google Reader). Add all this together and Google has a pretty robust picture of your social connections—and because it’s constantly crawling the Web to build its search engine, it can easily pick up what you do on any brand-new network that comes along. This suggests a long-term counterweight to Facebook’s power: As long as people keep commenting and voting and writing on sites other than Facebook, Google will be able to build a social network of its own.

On the other hand, Google doesn’t have access to the motherlode of your social activity: stuff you post on Facebook itself, data that is closed off to mining from most other companies online. Every time you press the Like button or use one of Facebook’s plugins to post a comment, you’re telling Facebook something about yourself and your friends. What’s more, Facebook’s reach keeps extending. Today, many people connect their activity on a host of sites—including Twitter, Flickr, Quora, Amazon, and Yelp—with their Facebook accounts. They do so because it makes intuitive sense to keep one social network—maintaining separate networks on different sites is too much work. If we’re sticking to one network, it makes sense to stay where all our friends are—and that’s Facebook.

This will be especially true if Facebook adds better tools for maintaining discrete groups within our larger friend network (which it already does quite well). In other words, hey, maybe Facebook already has this social-networking thing all wrapped up. We don’t know what the site will look like by 2016; it’s possible that, with all the ways it’s infiltrating the wider Web, Facebook.com will be just one small part of the Facebook empire. You may be using Facebook wherever you are online—and no other network will matter.

Why is any of this important—why do these Web giants want to catalog your interests and relationships? There’s an obvious answer—because doing so allows them to sell ads targeted to you—and a less obvious one: Social signals are becoming the primary organizing structure of the Web. Today most of the links you see online are determined by editors or algorithms—that is, by people who create sites manually, or by Google, which uses computers to guess what you might be interested in. But both these methods are imperfect. The people who create Slate’s home page every day are just guessing what you’d like to read. Google, meanwhile, serves up thousands of links in response to your query, and even though it’s often right, it’s far from perfect. Web companies see social data as the solution to this problem: That trail of Likes you’re leaving around the Web forms a picture of your deepest desires. With this picture, sites of all kinds—news sites, shopping sites, travel sites—can tailor themselves to your interests. In five years’ time, you and your dad may visit the Huffington Post and not see any stories that overlap. The site will know, based on your social network, exactly what you want to read.

This isn’t really a novel idea. “Link analysis” was at the heart of PageRank, the breakthrough algorithm that powered Google’s revolutionary search engine. When one site linked to another, PageRank saw the link as a recommendation; the more inbound links a site garnered, the higher it tended to appear in Google. But what’s a link? It’s one human being’s decision to tell other human beings that another page on the Web is important—in other words, a social signal. Google’s breakthrough was in recognizing that social signals can be a very powerful way of organizing the Web. It was the start of a $100 billion company.

By analyzing our social relationships in much more detail, Facebook is looking to do something even more revolutionary. Tell me what you think of the Facebook revolution—do you look forward to the social-networking future, or do you fear it? Is Facebook here to stay, or do you think we’ll move on to something else? Let me know in the comments below.