This is a really smart move by Google. This starts to eliminate the need for corporate social networks (like Yammer), and lets businesses take advantage of all the integrations that are happening with the other Google apps. As someone who has used internal social networks like Yammer at previous companies, I can honestly say that they are surprisingly useful - it gives other employees the forum to share interesting and work-related content, and provides a place for basic discussion on internal topics with a wide audience.