From looking at these reports, I still can't find their definition of a user (NYTimes reported that anyone using YouTube is thrown into the Google+ user pool, for instance). Also, this is unaudited data.
And there is something off with this data. It contradicts the comScore report, which showed people spending a few minutes per month on Google+, mere seconds per day. However according to Google, their users are now active 5.6 hours per month (only an hour or so less than Facebook!) and a few months ago they were active 4.2 hours per month. So somehow between January and March there was a massive (~1,000%) jump in activity across the board for all of its users, from a few seconds to 9 minutes a day. And after "a few" more months its at 12 minutes a day.
Here's Facebook's definition of a user:
"An active user is someone who has visited Facebook.com and logged-in (or been logged in) or who has taken an action with a Facebook feature (e.g. clicked like, etc
). If the user doesnt do any of those things for 30 days, they arent considered an active user. If they only see social plugins across the webeven if those social plugins include social context such as friends photos, friends likes, friends recommendationsbut doesnt click anything, they are not an active user."
That Google has been so hesitant to define its user suggest the real numbers aren't very pretty.