Based on a single, unnamed source, the Wall Street Journal says Microsoft is about to buy Yammer for $1.2 billion. Microsoft’s SharePoint enterprise collaboration software is notoriously difficult to deploy. The much lighter-featured Yammer – with its social UI and freemium business model, and with some integration to SharePoint, SAP, Salesforce and others – is the opposite. GigaOM Pro analyst Thomas Vander Wal notes that SharePoint implementers have discovered that SharePoint’s own social components have “too many dead ends,” but that Yammer’s conversion rate to paid customers might be too low for an IPO. And it might indicate that, while Yammer can demonstrate social utility to customers, its premium features aren’t worth it. Still, Thomas isn’t sold on the potential combo as a perfect match, and SharePoint ecosystem players (NewsGator, Telligent) might feel the resulting competitive threat more than the big social CRM wannabes.