To my understanding uploading documents MANUALLY to iCloud is not possible (before it was possible with MobileMe's iDisk). Only if a program supports storing files in iCloud you may choose to store it there (or locally on your hard disk)
You would have to use a third party solution (like the free Dropbox or Wuala ) to share documents between computers (or computers and iOS devices as they also offer Apps for iPhone/iPad).
christian
PS: as Apple writes on their website once you habe an iWork app on your iOS device you should be able to transfer it from MAC to iPhone/iPad.:
iCloud makes it easy to move Pages, Keynote, and Numbers documents between your computer and your iOS devices. Just sign in to icloud.com/iwork in any modern web browser, and all your iWork for iOS documents will be there — complete with your most recent edits. Click a document to download it in iWork ’09, Microsoft Office, or PDF format. You can also drag and drop any iWork ’09 or Microsoft Office document from your computer into one of the iWork apps on icloud.com, and it automatically appears on all your iOS devices, ready for you to review, edit, or present.
Message was edited by: Christian Theussl