The new interface has a vertical navigation bar that lets you reorder and hide apps. When you mouse over an app, Google+ shows a list of quick actions. This change will make it easier to add third-party apps in the future.
There are two new pages in the navigation bar: a hangouts page that lists the invitations from the people you've added to your circles, as well as a list of popular hangouts and an explore page for "what's hot".
The list of circles is now displayed at the top of the page, the search box is larger and the chat gadget has been moved to the right sidebar. When you resize the window and there's not enough room to display the chat sidebar, it becomes a floating panel.
Google+ conversations borrowed the old card interface from the previous versions of Gmail, while thumbnails for images and videos are bigger and include captions.
The profile page now accommodates bigger photos, so it's probably a good idea to upload new photos.
Vic Gundotra, Google Senior VP, says that there are 170 million Google+ users, up from 90 million users 2 months ago. That's a really impressive achievement.
{ Thanks, Jérémy. }