In a response to Gartner's forecast, a Microsoft spokesman said that "despite the availability of other productivity solutions in the market, Office 2010 has become the fastest-selling version of Office in history and we're seeing tremendous interest from businesses of all sizes in Office 365, our cloud productivity offering."

"Microsoft Office offers an enterprise-proven, unsurpassed productivity experience that is delivered on our customers' terms -- whether on premises or in the cloud. No other vendor can match that," the spokesman said.

Cain, in his report, cited a number of things Google has to do to win more enterprise businesses. Among other things, he said the company must deliver new features on schedule. Another obstacle for Google is a lack of transparency, which is a problem affecting the cloud in general, he said.

"Google remains especially opaque, refusing to share details about the proprietary code that underlies access control and privileged access mechanisms, and it shares only minimal details about the degree and form of offline backups that are used to recover from outages," Cain wrote.

Google recently announced that 4 million businesses use its Google Apps software and another 5,000 adopt it every day. The company didn't provide a breakdown on those businesses by size.