Google+ will be integrated through a widget on the Gmail sidebar where you will be able to see the most recent Google+ status updates add them to your Google circles.
“We’ll be rolling out all of these changes over the next few days to Gmail, Gmail Contacts and the ‘standalone’ version of Google Contacts at contacts.google.com,” Google engineering director Mark Striebeck said in a blog post. “Please note that Google Apps users won’t see the Contacts updates quite yet, but we’re actively working to make them available.”