I'll make a friendly $100 wager with you that Google will not have more active users on Google+ than Facebook has -- as reported by each company, a reputable publication, or measured by a public analytics firm -- 5 years from now.
Google's key to driving adoption is going to be integration of all of their services into Google+, which means that they have very natural and robust funnels for acquiring a userbase, so long as their tools are integrated properly.
Given the money that Google is pouring into this, and the incentive structure for engineers and teams at Google, i have no doubt that they will come up with clever ways to make their tools more social.
What does it mean to have social products? To tap into a users social network? That is what Facebook offers to any company that wants, and that is why 2/3rds of websites now have a Like and Facebook Connect button on them, it is very easy for any service to attempt the social route by tapping into the thing that only Facebook so far has, the social network.
Google cant engineer a social network using code, a social network requires specific steps to be carried out in perfect order, it cant be done overnight, you need to build smaller networks and connect them to larger networks as time progresses. It takes a long time, years even.
Reddit is social, hackernews is social. None of them have what Facebook has, real world information about living people and their relationships. Here on HN I could have 5 or 6 accounts and no-one would notice, HN, reddit and any other "social" product does not have relationships between humans. Google mail is close to a social network, except the fact that email is mostly used for business and so is most suited for something like LinkedIn, I personally have more companies mailing me than my friends. If I tomorrow made a new google mail account and began using it instead of my old one, would google be able to tell? Facebook for sure would.
New? What rock have you been hiding under?
Facebook's goal is to supposedly map out all real world social connections, and i would first say that such a goal is a pipe dream, and second that if you judge facebook by that criteria, that almost all services will fail to meet it.
I'm betting that Google+ will get more than just the early adopters.