CloudOn's app supports Microsoft Word, Excel, and PowerPoint. You can create and revise files from all three applications, either locally or from a cloud-based service. CloudOn offers access to Dropbox, Google Drive, Box, and Microsoft's own SkyDrive.
Thanks to an update to the app from last December, you can open and edit any Office document stored on SkyDrive. Assuming you've set up SkyDrive to sync with your local documents, any changes you make to a file are automatically propagated both locally and online. That's the same benefit that an Office app from Microsoft would presumably provide.
My only gripe with the interface is that the space for your actual document shrinks dramatically when you tap on the screen to segue into edit mode.The interface itself offers the familiar Ribbon interface first introduced with Office 2007. You won't find all of the commands and features found in the full desktop version of Office, but all of the core ones are in place.
The Ribbon and the keyboard take up most of the space, leaving little left for your file. But you can still focus on revising just one section or paragraph at a time.
The big selling point for me is the synchronization with SkyDrive. I don't know what Microsoft has in store for its mobile Office app, assuming it ever launches. But CloudOn's Office app works. It's free. And it's here now.