In the months leading up to the Office 365 launch in June, BPOS suffered several significant outages. If they become a recurrent problem for Office 365, sales could suffer, analysts say. Most cloud providers have experienced outages, but Microsoft has created higher expectations for its hosted software by saying it has more experience and a better understanding of business needs than its rivals.

Unlike cloud-only suites such as Google Apps, Office 365 is designed for hybrid environments. To use it both in the cloud and on the desktop, CIOs would need to deploy compatible versions of Microsoft's desktop and server products.

Forrester Research analyst Rob Koplowitz notes, meanwhile, that it's hard to integrate on-premise third-party tools with cloud suites. Therefore, CIOs must weigh the benefits of cloud suites against the difficulty of integrating them with software from other vendors.

"There is no doubt that Office 365 is going Apps," Gartner analyst Matt Cain said via email. "It is a savage competition that will pay benefits for the industry," such as faster innovation and lower prices.