Just to be clear, Dropbox is the only supported tool for syncing with iOS devices. iCloud and other services are fine for syncing between Mac OS devices, provided that the precautions described in this article are taken:
scrivener.tenderapp.com/help/kb … c-services
(Why the disparity? Because Macs have both real multitasking and real disk management tools, while iOS has neither.) (Which is one of many reasons to be skeptical about suggestions that iOS will ultimately replace Mac OS.)
Katherine