If you opt-in -- Dropbox is stressing the "early access" or still-in-development nature of the plug-in -- you get a Dropbox badge in your PowerPoint or Excel documents that lets you see who else is collaborating with you, see if there's a more recent version (and refresh the document if there is), or generate a link to share the document, all without leaving the program, per the official blog entry.
Dropbox's strategy has always been about being the glue that holds together the BYOD/mobile/social world of multi-environment apps and devices. Using Dropbox for storage, it doesn't matter if you're trying to access your documents from an iPhone, Android, Windows Phone, PC or Mac -- the content is just there waiting for you.
Building that functionality straight into Microsoft Office is another step toward that same goal: I can be on my desktop, plugging away in the familiar, comforting embrace of Microsoft's ecosystem, and my colleague can be editing the same document from within a browser on his Chromebook. We're all doing work in the way we want to, and the content is just there. Combine this with the Microsoft/Dropbox partnership that makes Dropbox a preferred, built-in option for storing documents in Microsoft Office 365, and you have some kind of funky synergy going. It's definitely an edge for Dropbox over more enterprise-minded rivals like Box.
As an added bonus, the more people in the office working this way, the more likely the CIO will eventually feel forced to shell out for a Dropbox for Business account, which is all according to Dropbox's sinister master plan.
Project Harmony is a work in progress, and Dropbox is promising that more desktop and mobile app integrations are to come. But the name really says it all: Dropbox sees the way forward as helping users work together in perfect harmony.