One of my favorite features of Mountain Lion to demonstrate so far has been the iCloud Document Library. This is a way to store your iWork, TextEdit, and Preview documents in iCloud so that they are immediately accessible from other Macs on the same iCloud account as well as on connected iOS devices.
TUAW blogger and developer Erica Sadun told me the secret behind this on Wednesday. If you go to your Library folder and open the "Mobile Documents" folder, you'll notice that the name of the folder changes to iCloud (see screenshot below). That's where all of those documents are saved, and it's even possible to just drag items into the folder to add them to your iCloud Document Library.
In compatible apps, you'll find that selecting "Open" from the File menu displays a new Finder Open dialog with buttons for iCloud and "On My Mac". Selecting iCloud displays a very iOS-like dialog showing all compatible documents. Drag one document onto another, and you can create a folder -- another iOS feature. Likewise, selecting "Save As" from the File menu gives you the choice of saving a file to your iCloud Document Library.
The updates to Pages, Numbers, and Keynote on the morning of July 25, 2012 added these capabilities to iWork '09. As an example, the same Open dialog with buttons for both iCloud and On Your Mac appears (see below).
Users of the iWork.com beta will find that documents that they saved to that service magically appear in iCloud without requiring any work on their part.
Is iCloud turning into a replacement for Dropbox? With the present pricing plans and capacities available for both services, I'd say the answer is "no". But for those who have minimal cloud storage requirements and who are using the handful of apps that currently take advantage of iCloud Document Library, iCloud and Mountain Lion are a well-designed and implemented alternative.
Check out all our Mountain Lion 101 articles for more tips and features from the latest version of OS X.