SharePoint, which started off as a document management system back in 2003, also now includes Web 2.0 features such as blogs, wikis and social networks , which were added in 2007. While users access SharePoint through a Web-browser, companies typically host the SharePoint server software themselves, onpremise.

You won't find Microsoft executives calling SharePoint Online a SaaS (software as a service) offering. In fact, according to analysts, that phrase doesn't fit into Microsoft's lexicon of technology terms. Instead, it's called "software plus services." At its core, software plus services essentially means that Microsoft will provide online portals and will host the data, but in order to manipulate the files that reside there, you'll need the Microsoft Office suite installed on your computer.

It's a similar idea to its Office Live product, currently in public beta, which also requires users to have their versions of Office on their computer in order to work on files.

Both Office Live and Microsoft Office SharePoint Online differ from fully Web-based, SaaS offerings like those from Zoho and Google Apps, which allow users to author, edit and share documents all online.

According to Rob Curry, director of Microsoft SharePont, software plus services means letting businesses decide what data they are willing to let a vendor host and what information must never leave the company's walls.

"It's not all or nothing," Curry explains. "There is certain information they want to keep offsite and certain information they want to keep onsite for compliance reasons."

According to Rob Koplowitz, a principal analyst with Forrester, that message will resonate with CIOs who have had difficulty envisioning putting all their data into "the cloud," but would be happy too offload less sensitive stuff that takes up server space and costs money to maintain. Sensitive financial data, for example, might not be a prime candidate for storage in the cloud.

"They can see letting certain types of users accessing certain types of data from a cloud version, and others using an on premise version," Koplowitz says.