The new beta versions of Pages, Numbers and Keynote were released shortly after a ninth beta of iTunes 10.5 and bring support for the new Documents and Data service that will be included in iCloud.
If you create a document in one of the iWork apps it becomes instantly available on an iOS device or via the iWork web app, which can be accessed via any browser. Manual saving to your local machine or a cloud-storage service isn’t necessary.
iCloud was opened to developers in August and when it is publicly released – possibly tomorrow, or perhaps later – users will get 5GB of free storage for documents, backups contacts and calendars. An additional 10GB will cost $21 per year, $42 for 20GB and $105 for 50GB.