The June 2011 issue of BSD Mag has an article “Introducing FreeNAS 8.0” on pages 14-18. You can download this issue for free here. The publisher has also made this article available as a separate PDF which is available here.
The article describes:
* the reasons behind the redesign
* differences between .7 and 8.0
* an overview of the graphical interface
* FreeNAS 8.0 resources