Editor’s Note: This post originally appeared on Peter’s personal blog and was republished here with his permission. It is a follow-up post to Mike Troiano’s piece on Google Plus.

After a much-ballyhooed private beta launch that’s reached 18 million users, where does Google+ fit into the social networking landscape? Or better yet, who should really be worried about the search behemoth’s social networking arrival?

Google+ has drawn numerous comparisons to Facebook and the popular theme seems to be that Google is poised to take on Zuckerberg’s 700-million+ user empire. Facebook’s continued work to block contact exporting to Google+ is feeding that fire.

Still, I’d argue that LinkedIn, and to a lesser degree, Twitter, should be much more concerned with what’s brewing with Google+.

Google’s already suffered two well-documented stumbles in the social networking space over the last few years with Wave and Buzz, but it’s different this time around. Google+ quickly gained street cred with the social networking uber-gurus, and as the invitations trickle down to garden-variety social media experts and everyday folks, the hype and chatter continues to build.

But the question is, why? What has Google achieved with Google+ (or should we really call it Google Circles? Or is that just one feature? Paging the Google marketing department…) that has everyone so excited? Will it really be a case of “meet the new boss, same as the old boss” with Google regaining online supremacy and toppling Facebook?

I’d submit instead that digital-savvy people are more scared than anything. I know I am; I feel like Google’s finally gotten it (mostly) right, and as I result, I need to drop anchor in case Google+ explodes. The Circles concept is much more analogous to our real-life relationships than Facebook’s “friending” mechanism. People are quickly growing more comfortable with the idea of connecting online with nearly or complete unknowns, but still want privacy controls to filter their outgoing missives and basic data set. Facebook, despite continuously changing the rules of engagement, has failed to make this easy.

The Circles concept resonates for those of us with geek sensibilities, and so far we’re embracing Google+. Given the buzz, as soon as Google+ brand pages are available, I’ll launch one for the Boston Celtics, and add the +1 button is coming to Celtics.com as well. I presume similar organizations and brands will follow suit. Our new Google+ Celtics page won’t catch our five million Facebook “Likes” anytime soon, but if people are going to be discussing the brand there, we need to have a presence.

But here’s the big reason to watch Google+: Since Google’s already the reigning champion of search, it stands to reason that Google+ profiles could soon become the new social directory of the Internet. It’s somewhat surprising that it’s taken Google this long to figure it out, or at least to unleash it on the masses. After all, LinkedIn profiles and Twitter posts have been peppering Google’s search results for some time, and even the most pedestrian of social networkers understand that their contributions to these networks are highly searchable by default; in fact, that’s the whole point of LinkedIn for many of its users. So it stands to reason that Google’s been contemplating this step for a while.

But as I finally got around to fleshing out my Google profile this week – I’ve never been a Gmail guy so this was a fresh start for me – I really tried to think about what makes Google+ different, and why it’s so critical to participate. And despite the shiny new features like “Hangouts” and “Sparks” (something sports brands should keep an eye on), I keep coming back to search engine results.

Simply put, if you haven’t Googled yourself in a while, drop everything and do it now, or at least after you’ve finished reading here. Search results are constantly in flux, and you’d have to imagine that Google will eventually rate their own profile pages higher than third party results for a bunch of obvious reasons. The most obvious of which being dollar bills. So far, Google+ profiles are devoid of advertising. But how long will that last? Google draws almost all of its revenue from advertising. They literally make billions of dollars on this each year.

You do the math.

With 100 million users making white-collar wages, LinkedIn has built a highly-targeted audience that should carry incredible advertising value. Obviously, Google is interested in competing for this audience.

But back to what it all means for you. When it comes to basic personal branding, LinkedIn is the dominant platform. Chances are, if you meet a young professional today, you can track them down instantly on LinkedIn. But the profiles I’ve seen to date on Google+ appear largely professional in nature, and Google+ looks and feels much more like LinkedIn than Facebook, and that’s with good reason.

Unlike a Facebook page, where nightlife pictures are de rigueur and dominate the photo uploading activity with the understanding that they’re, um, mostly private, a Google+ profile seems inherently intended to be public. Unless you really want those college keg stand pics coming up in search results against your name, Google+ probably isn’t the place for them, even with privacy settings in place.

The young professionals set, and for that matter, anyone else who has a vested interest in building an online brand, seems to get that and be comfortable with it as well. If Google+ results are going to eventually be the first thing that comes up when you’re searched, you’d better control what shows up. You’re already working on your brand now with LinkedIn, a Twitter feed, and maybe even your own blog/portfolio site. But if you want to control it tomorrow, get your Google+ presence sorted now.

LinkedIn launched several years before the social media explosion, and because of that, most users are still reluctant to connect with people they don’t know. LinkedIn explicitly tells them not to do it, and for most people, that makes sense. A LinkedIn profile is a reasonable facsimile of a resume, and exposes quite a bit about one’s identity. With that in mind, LinkedIn profiles are typically kept private to users outside your network.

LinkedIn is vastly dissimilar from Twitter. There’s the strong perception that by connecting with someone on LinkedIn, you’re vouching for them; drawing that conclusion from a Twitter follow is a much greater stretch, although a retweet tends to convey that connotation.

That perception probably hurts LinkedIn’s growth, and it’s unlikely to change unless LinkedIn takes the Circles approach and acknowledges the complexities of interpersonal relationships. Currently, when you fill out the brief form to invite a connection on LinkedIn, the site warns you “Important – Only invite people you know well and who know you.” When you click on this message, a pop-up window informs you, “Connecting to someone on LinkedIn implies you know them well.”

Google+ goes in the other direction, offering pre-fab circles called “Following” (“People you don’t know personally, but whose posts you find interesting”) and Acquaintances (“A good place to stick people you’ve met but aren’t particularly close to”), recognizing and encouraging the growing trend Twitter really popularized: following people and personalities that you’ll never likely meet in real life.

With all of that in mind, mainstream adoption will take time for Google+. Launching their iPhone app on Tuesday was another step in that process. Still, the average social networking user will need a compelling reason to find time for Google+ updates.

With all of that in mind, I asked an old college pal who’s in one of my Circles what he thinks of Google+ and its potential staying power. He Facebooks as much as the next guy, but isn’t on Twitter, just learned about Instagram last night, and has yet to do anything significant with his Google+ account.

His take: “I just don’t get it. There’s enough social media crap going on anyway. I mean, people keep adding me and I’m like, OK. Whatever.”

Sobering? Perhaps. Time will tell if it gains mass traction with the non-digerati. Still, amassing 18 million users in a two-week private beta is encouraging, and a reality check for the Foursquare fanboys out there who recently celebrated 10 million users after two years. While LinkedIn should officially be on watch, I don’t think Facebook has much to worry about in the short term.

That said, I’m sure they’re paying attention like the rest of us. Close attention.