iA Writer for iOS and OS X adds full iCloud folder support, Mountain Lion compatibility | The Verge
The iOS version matches the file system capability, allow the creation of iCloud folders by dragging and dropping individuals files atop one another, and also features what Information Architects is calling "responsive typography": basically, it improves the quality of text whether users are taking advantage of a Retina-caliber screen or an older display. The updates for both platforms are available now, though to take advantage of all of the new features in the OS X version you'll need to be running OS X Mountain Lion — which according to Apple should be just around the corner.