In Pictures: OS X Mountain Lion arrives - the top ...
Documents in the cloud
Another iOS inspiration, developers can iCloud-enable their apps to store and retrieve documents directly from Apple's iCloud service for access on both Macs and iOS devices. As in iOS, an app sees only its files, though you can easily move or copy them among other apps and between the Finder on your Macs, where all apps can see them (unlike in iOS).
There is a gotcha: Only apps sold via the Mac App Store may use the iCloud Documents APIs. Preview and TextEdit are among the built-in apps that support iCloud Documents; Apple's iWork suite has been revved to do so as well.
In Pictures: OS X Mountain Lion arrives - the top 25 features