I agree with neon.
Take a note out of Dropbox's book. Add it like another Google feature, that can be tied into all of google's other features. This would create the one stop storage option that starts out small, through invitations and people accepting you get a bigger slice of the pie. Google loves keeping things on an invitation level, as well as a free version with a professional version purchase option, so I think its right up their alley.
Google buy Dropbox, and call it a day.
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