I think Google+ biggest bet right now is to spot, or introduce, the way people will live the web tomorrow. Changing it from Search to Discover.

And no, it can't relay completely on our friend's interests (à la Facebook) cause they're their interests not ours.

We'll probably stick much and much more to our beloved communities (topics, not friends) and start every web-related activity from there. That's something Google can't let Facebook win on.