“Apps isn’t for everyone,” Sinha writes. “But in the last week alone 38,000 businesses decided to give it a try. Maybe you should too.”

Google claims more than 3 million businesses use Google Apps, and the company just launched a line of Chromebooks, Web-only laptops that don’t require Google Apps but may be effective for Google Apps customers.

Best Microsoft MCTS Training, Microsoft MCITP Training at certkingdom.com

Microsoft’s publicly stated numbers are a bit higher: 750 million active users of Office, and installations on 1 billion PCs, although Microsoft doesn’t detail how it arrived at those calculations.

Microsoft CEO Steve Ballmer is scheduled to talk to press in New York City Tuesday to announce the launch of Office 365. Microsoft is likely to argue that it’s better suited than Google to providing a full-featured and secure office experience, whether in a customer’s data center or in the cloud.

But there’s room in the market for both, and Google has won some converts. Sinha hopes Google’s cross-platform capabilities will win some more.

“Office 365 is optimized for Windows-based PCs and devices, which reduces your flexibility,” Sinha argues. “Our applications are designed to work well on any device, on any operating system. Desktop, laptop, Chromebook, tablet, smartphone. Windows, Mac, Linux, Android, Blackberry, iOS, Windows Mobile.”