In the comments of this blog post it says that the CR-48 won’t get the Aura update yet. It may come in future updates under the Dev channel.
http://googlechromereleases.blogspot.com/2012/04/dev-channel-update-for-chromebooks.html
http://arstechnica.com/gadgets/reviews/2012/04/hands-on-getting-work-done-with-googles-new-aura-interface-for-chrome-os.ars//cdn.embedly.com/widgets/platform.js