Yes, active users would be better. It's still useful though to have users registered. At some point it'll hit critical mass and that bar at the top of the page will start lighting up with notifications.
I had a linkedin account for years before I paid any attention to it. Eventually the emails started rolling in to engage me.
LinkedIn is probably a good comparison. I too heard about it years and years ago, but only got around to signing up for it this year. I figure Google+ will be similar for most people, as long as Google keeps the updates coming like they have been.
I had a linkedin account for years before I paid any attention to it. Eventually the emails started rolling in to engage me.