Since dropbox knows which files are being worked on, I don't actually think it needs to be inside of the application, it could just as well be a standalone overlay. The "sneek peak" screenshot does indeed look like an overlay that pops up when you open a file and which tracks the collaborative status. It also seems like it adds messenging functionality, which I must admit looks neat - pointed messenging functionality tends to be a lot more productive than general purpose messenging.

Still right now if you edit the same file from different locations at the same time you will end up with conflicting copies. I wonder how/if they solved this.

Yeah, I see that. It would be really nice if you could see the other people editing the file, what they are editing, and a way to diff versions. (Similar to Google Docs editing) This would definitely require some sort of data API.

I could see this being really interesting while collaborating on a complex 3d model or scene. I change one spot of the scene and it propagates to everyone else using the application.

From what I can see there, that is a general windows overlay and not an intergration into Office, which would be much more ugly and afaik would not leak outside the window. So I guess it goes a bit like: DB watch files, find pid of process editing them (PowerPoint w/e) and they overlay a window.