If this is at all representative, I suspect the percentage of active users to total users is pretty abysmal.
Although G+ still has way fewer posts than Facebook, I suspect that it would need a much higher post rate than Facebook to appear as "active" to users.
I find G+ posts to be generally of much higher quality, especially shared things.
I had a linkedin account for years before I paid any attention to it. Eventually the emails started rolling in to engage me.
I like how Google PR is working hard to spread the message, but I ain't seeing what they are selling. Don't get me wrong: I'd love to see FB have some competition. But G+ isn't cutting it as yet.
I bet that in the early days of Facebook & Twitter, they were not releasing their number of active users either.
I remember when I signed up for Facebook in 2007. None of my friends were there. They were still on Friendster.
History should teach us a lesson that growing a social network takes time.
it's not comparable.
that being said I think their rate of growth is very good. i also like the G+ UI a lot more, it's pretty good.
The only thing I dislike is that it's one more thing that Google fully control and doesn't really open up.
Note that I actually dislike both for privacy reasons as well.