Gmail received a minor update today that allows you to manage your Google+ contacts directly from the sidebar. While this is convenient if you're a fan of the social network, it's particularly helpful if you want additional context about your Gmail contacts.
When you add one to a circle in Google+, a little label will show up with the name of that circle. This can help you get a better idea of who this person if they're not someone you interact with regularly. Circles can also help inform you of the content of the email, if, for example, the person contacting you is a member of your hiking club.
Additionally, the new Google+ integration will keep contact information up to date automatically. If you're tired of adding or changing phone numbers, addresses and other details of your contacts, you can let Gmail take care of that by pulling information directly from Google+.
Check out Google's official post for more details and screenshots, or just log into your Gmail account to check out these new features. (Note: The rollout is still under way so it may take a few days before you start to see them.)
Gmail and Contacts get better with Google+ [Official Gmail Blog]