You all have noticed the new black Google navigation bar. It'll be your connection to Google+. You can share what's on your mind, view your Google+ notifications, access your profile, or jump to a variety of other Google products.
One of the most interesting feature of the bar is notifications:
"When you receive a notification, the notification area in the Google+ bar will turn red and show the number of new notifications.
If you click the notification area in the Google+ bar, you’ll see a summary of your recent notifications. When you click a notification, a preview of the event that generated the notification will appear in the drop-down menu. You can take action on each notification right from the notifications menu, like commenting on a post or adding someone to a circle."