It’s a tough situation and its one that Apple has failed to lead in because a successful strategy must go beyond the borders of Apple’s white picket fence. In other words, they do much to oversee the experience of their platforms, but an iCloud solution that works would have to succeed in the open internet with countless web applications that see no need to create native applications for the Mac. It’s a problem and that I believe is the main reason the whole iCloud experience lacks a solid implementation.

http://www.literatureandlatte.com/scrivener.php

http://developer.apple.com/library/mac/#documentation/General/Conceptual/iCloudDesignGuide/Chapters/iCloudFundametals.html

We see that the sandbox and ubiquity containers are separate. Then further down the dev article you’ll see that you can have multiple apps accessing a single ubiquity container (such as a free version and paid version) (heading “Configuring a Common Ubiquity Container for Multiple Apps”)

Apple may not allow apps from different developer ID to share common UC but it’s feasible that that support could be added in the future so long as the proper security is in place.

I have high hope for iCloud but until it matures I think a multi-cloud solution is what most of us are going to need.

They do both backup and file sync in the same app.

I think you would be missing something if you don’t add them to your search.

I am a Mac guy that loves Mac-only stuff. I don’t think they have a Windows version yet.

When Scrivener for iOS comes out, you might want to look into using it for your writing. Pages is designed for layout, while Scrivener focuses on writing itself, particular for books or multiple articles in a series. And I suspect it’ll offer either Dropbox or iCloud synching, so you can take your choice. Also, there are already OS X and Windows versions of Scrivener, so you can move between platforms.