SharePoint Online just released a significant update. These updates appear to be geared at supporting larger Enterprise customers.

The major changes include:

  1. Increased Organization Scalability: The previous version could support up to 20,000 user objects in Active Directory. The latest update increases that to 500,000.
  2. Reduced Administrative Costs: The latest version enhances the "undo delete" capabilities in the Recycle Bin. Now full site collections can be restored, in addition to the existing ability to restore sites, documents, lists, and list items.
  3. Easier External Collaboration: SharePoint Online gets better for extranet scenarios. External users can now use their own email address once they associate it with Windows Live ID. Then the external user can sign in with their standard business email and password.
  4. PDFs: PDF files now open directly in the browser (no downloading required) and updates are synchronized with SharePoint Online automatically.

[Source]