The ability to add your own user groups is new in Joomla 1.6. You can also add users to one or multiple user groups. Watch the Joomla 1.6 video on user groups to find out more.
There are a number of changes to the toolbar in the Joomla 1.6 Administator, particularly in edit screens, to bring button names and behaviour in line with what you are familiar with in a desktop application. Watch the Joomla 1.6 video on the toolbars to find out more.
The Joomla 1.6 Adminstrator menu has undergone some changes. Users now has its own menu that includes adding groups and access levels for viewing content and other features have been moved around. Watch the Joomla 1.6 video on the Administator menu to find out more.
Joomla 1.6 includes several new features for modules. You can time a module to be published between two dates, and you can set modules to be excluded from particular pages. Watch the Joomla 1.6 video on modules to find out more.
Joomla 1.6 includes a new feature called template styles. This gives you the ability to use a single template in many different ways by saving different sets of options as a style. Watch the Joomla 1.6 video on template styles to find out more.