"There are other services out there that let you create and collaborate on documents," Kinsel says, "and there are others that support sharing, discussing and discovering documents. But what makes Docs special is it's the only service that supports the complete document lifecycle. That coupled with seamless integration of Microsoft Office 2010 and Facebook makes Docs the best possible document service for the Facebook environment."

The question, then, becomes whether a "social-productivity experience" is something people actually need -- whether collaborating on documents is an activity users want within their Facebook worlds.

Microsoft and Facebook are clearly betting that it is. Only time will tell if they're right.

is a PCWorld contributing editor and the co-founder of . He's on Facebook: