According to Google [1] "300 million people active in just the stream" which means that either:
1) author is wrong,
2) Google is considering the fact of being logged into G+ and, say, using Google search counts, or
3) 98% of activity is made private.<p>I bet it's a mix of all three with emphasis on something 2-ish. ;]<p>[1] <a href="http://googleblog.blogspot.com/2013/10/google-hangouts-and-photos-save-some.html" rel="nofollow">http://googleblog.blogspot.com/2013/10/google-hangouts-and-p...</a>