The demonstration site lets users experience the look and feel of Plone 4 as well as check out its ease of use and new features. Its a great tool for demonstrating Plone 4 without needing to do a local installation and for folks to look at the changes since Plone 3. The site lets users log in using a variety of roles so they can see the difference between what users, editor and adminstrators see when working in Plone 4.
You can access the demo site at http://demo.plone.org .