Oddly enough, the key reason why I believe Google+ will overtake Facebook is because, in my opinion, Google got groups right where Mark Zuckerberg suggested that Google got groups wrong. That is: Google+ allows you to create groups where the members of the groups don’t know which groups they are in.
Several days ago, Mark Zuckerberg said: “The definition of groups is . . . everyone inside the group knows who else is in the group” (http://techcrunch.com/2011/07/06/zuckerberg-dig-at-google-ci...) Because Google+ had just been released, and as Zuckerberg had been asked about it, TechCrunch’s Eric Schonfeld assumed (probably correctly) that Zuckerberg’s statement was referring to Google+’s circles.
In Google+ you grab icons that represent people you know, and then drop them into circles, where everyone in the circle shares a common communication thread. Some circles are pre-created like ‘Friends’ and ‘Family’, but you can make your own custom circles too. Also, you can put one person in more than one of your circles. You can be my 'Friend', and my 'Sailing buddy'.
If you add me to a circle, I know that you added me to a circle, and I am a party to activity within that circle. But importantly, I don’t know which circle I have been added to, or who else is in that circle unless they speak up.
As Mark Zuckerberg alluded to, that definition of a group seems counter-intuitive. I will admit, when it comes to a group like your soccer team, everyone knows from the outset who is in the soccer team group. However, after using Google+, I began to realize how much this functionality reflects real-world behavior.
Consider that person at your work that you think is just ok, but that is very fond of you. To this person, you are a friend, maybe even a true friend. Yet, to you, this person is an acquaintance, -a coworker. In face-to-face interaction, thankfully, the two of you never need to resolve this difference amongst yourselves. However, Facebook asks you two to agree upon whether you are 'friends' or not. This is not the case with Google+. In Google+ your can drop them in your coworker circle, and they can drop you in their best friend circle. No friction.
My least favorite aspect of Facebook is that everyone I know is a friend. Google+ fixes that for me. I think that Google identified the biggest problem with Facebook, and then solved it.
I like you. I want to maintain a connection with you. But, you are not my friend. I will put you in a circle that works for me, one that you are already in.