The rumor mill is working overtime with suggestions that Microsoft might be purchasing social networking provider Yammer for as much as $1 billion. But given Microsoft’s near-absence from the social landscape, that billion could be a bargain if it ensures the company’s relevancy as the social enterprise market accelerates.

Business Insider first broke the story that Yammer employees were discussing a possible Microsoft purchase since Monday – a claim substantiated by Bloomberg News today, which now says that the deal could be announced as early as tomorrow. Neither company is saying word one.

Yammer, for its part, is a well-funded ($140 million since 2008) company with 200,000 customers, including eBay and Ford. As recently as April 2012, Yammer acquired oneDrum, a file syncing service that emphases Microsoft Office document collaboration.

In other words, Yammer has proven (if somewhat limited) integration with the Microsoft ecosystem and serious enterprise adoption. Combine that with Microsoft infrastructure, Microsoft Office 365 cloud productivity, and Microsoft Dynamics CRM, and the synergies start to become apparent.

This is absolutely critical, as Microsoft’s chief rivals in the CRM arena – Salesforce.com and Oracle – race to see who can integrate more social tools and services more deeply into their portfolios. Just recently, Salesforce.com dropped $800 million on Buddy Media, while Oracle opened their wallets to the tune of $300 million for Virtue and an undisclosed but likely ridiculous sum for Collective Intelligence.

It’s a case of meet-in-the-middle. Salesforce.com specializes in cloud CRM, and essentially invented the term “social enterprise,” but has extended its play significantly to the platform-as-a-service space with Force.com and Heroku. Oracle is a database/CRM specialist that’s only recently affirmed its commitment to social and the cloud.

Microsoft already has CRM, PaaS and a general cloud strategy, but has absolutely no game when it comes to social. That’s going to be a problem if it isn’t already, as social media is increasingly lauded as productivity-boosting and engagement-heightening inside and outside the enterprise. If Microsoft doesn’t have it, customers are going to look elsewhere. Google, for example, is using the Google+ social network as the “glue” between the Google Apps suite of cloud applications.

Microsoft doesn’t have a highly prominent services organization, so my guess would be that Redmond buys Yammer and leaves it to channel partners to implement and extend. But just putting the basic bricks there – well, it makes more sense than Facebook paying $1 billion for Instagram.