There is an issue of compatibility of Windows and Mac. If there is a Dropbox file shared between Mac and PC and Mac owner creates there file using characters which are not supported by Windows in file name ( characters are \/:*<>| ) then Windows owner cannot see the file or folder (or files in such named folder). Actually Windows user even doesn't know about that he cannot see that. He is not even synchronizing those files. And Mac user does not know about it as well as Dropbox is not showing any issues with it.
I understand that this kind of error cannot be erased by Dropbox, but it would be quite beneficial for customers who are working in teams of Windows and Mac users can have feature of automatically showing if there is an error of syncing some files from cloud into their PC.