This is actually Google’s second step in this direction. Since March, Google+ users were already able to add people to their circles from inside the Google+ notifications email.
With today’s update, however, Google is basically bringing the full interactive Google+ experience to these messages. Users can now view, comment on and +1 posts from their inboxes. Responses from their friends will also appear in real time right inside the message.
These features will roll out to all Google+ users over the next week (and if you’d rather not get Google+ notification emails, you can also turn them off here).
It’s worth noting, by the way, that a number of startups, including PowerInbox – which we wrote about earlier this year – are also trying to make email more interactive and turn it into more of a platform. The PowerInbox browser plugin, for example works with Gmail, Hotmail, Yahoo Mail and Outlook and its API is already being used by a number of other email clients, including Unified Inbox, already.