Well, you don't get simultaneous real-time editing by multiple users with conflict resolution - but that's not why I use Dropbox for. In the last year, I had two documents where I needed to do that, and I used Google docs for that; but it's a very rare edge case for me. Frankly, in many real cases, I'd trust Word's track-changes+email workflow better despite its horrible usability - as when editing an agreement or technical spec, you don't really want to share everything with the "other side", so you need keep the comments and not-really-decided edits hidden; and you also want to review all their recent changes explicitly every time.

Most documents I work with need no conflict resolution as creator and viewer is strictly separated; but where proper collaboration is required, Google Drive won't cut it, I would want to have a proper version control system like git or similar.

There won't be Google Drive support for native-level editing of, say, Photoshop files, folders of code, audio data, or any data files edited by in-house built tools; but you can have a decent workflow where Dropbox syncs these editables between all your computers, and also allows others to read their latest version from a shared folder.