The major change is the introduction of a new left pane, which replaces the previous blue top bar. It gives a more optimized interface, as most new computer screen are now wide format. It also allows to display more items in the main page list.
The left pane items also now display the number of items they have, like the number of items in a Contact group or the number of posts in a given workspace.
Save and Cancel buttons are now displayed both on the top and the bottom of the screen in an edit page. In the previous version, it was only present at the bottom of the screen, which required to scroll down the entire page in case there was a long form, such as in the Projects and business contacts app.
An Enhanced dashboard, with bigger and nicer icons. Also the admin functions, such as user managementm settings and application management are located in a new left pane
Application management. There is a new link directly from the Dashbaord. You can now add / remove applications directly from your web accout in one page. In particular, when you have a business account you can add the personal applications if you wish, such as RSS News and Wikipedia.