Could it be that we don’t want to communicate with our coworkers the way we do with our Facebook friends?

If so, that’s not good for Microsoft’s business-oriented social network Yammer, which it bought two years ago for $1.2 billion. The network remains a major part of the company’s strategy, but the momentum around social media is not proving to be easily (or universally) transferable to the enterprise.

It’s not for lack of trying. Microsoft is throwing every trick in the book at Yammer, including tightly integrating it with its Office 365 platform. But whatever Microsoft is trying, it’s not bringing immediate results. (The strategy also feels suspiciously like Google+’s growth-hacking approach, which certainly isn’t the best sign of strong engagement.)

And the man who led Yammer to battle is out. David Sacks, the former PayPal executive who launched the company in 2008, announced he was leaving Microsoft this week in the midst of a massive company reorganization that includes 18,000 layoffs. In his memo to employees on his departure, he remained bullish about what he helped build.

“Today, thousands of companies are using social to transform their organizations, and consumerization is a major trend in enterprise software,” he wrote on Yammer (obviously). “So our original beliefs are no longer controversial. This stands not in contravention of the work we did, but as the ultimate testament to it. We all know how hard it was to get here.”

A Tough Egg to Crack

Sacks is absolutely right about that challenge, and bravo to Yammer for its success so far. That more than half a million companies have some sort of interaction on a network like Yammer is huge, especially when the competition—email— remains firmly embedded.

But here’s the question: Is half a million good enough for Microsoft? A lot more than half a million organizations use Office. The company has to do a lot more to push Yammer as a concept to make its big investment worth it. Microsoft clearly bought Yammer hoping to make it as mainstream as another of its big acquisitions, Skype. That won’t be easy.

Last week, The Wall Street Journal noted statistics from IDC that show the annual growth rate of enterprise social networks was around 23 percent per year over the past five years. Sounds good, until you realize that IDC reported the same stat as 42 percent just two years ago.

Furthermore, the WSJ highlighted Forrester research showing that more than half of employees responsible for enterprise social initiatives said that they’re still struggling with basic issues of adoption and engagement. In other words, they’re still at step one with most of the office—something highlighted by this recent CMS Wire piece on Yammer.

Eating One’s Own Dog Food: Not So Easy

Even internally, Microsoft’s dog-fooding process with Yammer was anything but smooth. The reason: Its employees already had several internal communications options, including a Twitter-like microblogging platform. Yammer was just one more thing. (Sound familiar?)

“It didn’t matter that Microsoft had bought Yammer for a considerable sum,” CITEworld‘s Ron Miller wrote last year. “It still took work to get employees to gravitate to a new tool and to make it part of their natural workflow throughout the day.”

Eventually Microsoft figured it out, claiming more than a third of its employees used the platform as of a year ago—not bad for a company with an employee base of 100,000. (Well, at the time.) Nonetheless, Microsoft’s experience highlights an important issue for enterprise social networks: They don’t have quite the viral properties that something like, say, Vine does.

If the social enterprise is gonna hatch, we either need better eggs or more eager chickens.

Counting Chickens Before They Roost

None of this is to point the finger specifically at Yammer. The problem here is a universal one—and, if anything, Sacks and company have probably done more to help solve it than any one platform.

They, along with Salesforce.com, have the real upper hand on this whole social-in-the-enterprise thing. And there are other players, such as Slack, Basecamp, Trello, and (my personal fave) Hackpad, that offer truly interesting ways to communicate with others within the workplace. Even mainstream social networks, such as Secret, want to get into the enterprise game. (Editorial opinion: Secret is an awesome network for pure socializing, but I’m skeptical about its enterprise odds.)

But we don’t use Twitter or Facebook or even our association’s private online communities the same way we use an internal social network. We communicate differently in a professional context, and too often we’re already set in our ways: We like to communicate with our colleagues via email or by phone.

I actually tackled this issue last year, and I certainly think it’s possible to someday end email’s reign as the business communication tool of choice. But the question is, are these technologies better enough than email? The answer, I believe, is not yet—though we’re a lot further along than we were even a couple years ago.

This creates a chicken-and-egg conundrum for many offices. If you’re the only person in the world with a fax machine, it’s not very useful, is it? It’s the same deal with every form of communication, ever, and a social enterprise platform is way harder to seed than, say, Facebook.

If the social enterprise is gonna hatch at Microsoft scale, we either need better eggs or more eager chickens. I’m betting that we’re more likely to see the former than the latter.

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