OK, as far as I could find so far the major, if not the only, advance Google+ have against Facebook is their circles concept. But I'm still a little confused what would be the right way to use them. The circles are great, I agree, they prop your networking up into multidimensional space. However in my opinion it's still a half-way solution. And here is why I think so.
1. The circles are sharing circles, not the reading ones. Or not? I create circles and put certain people in them to control whose streams I'm going to clatter with my posts. I'm sure that some geeks are absolutely not interested in my kid's photos, and my relatives are least likely would appreciate my nerdy essays in their stream as well. OK, that's how I understood the circles at the first glance. And it seems to work this way, I mean one-way. But why all my the same circles are used as filters for my own reading stream. Does it mean that I have to carefully redesign my circles to make use of them for my reading? Should I create a circle "most interesting" and add and remove people to it based on their posts' interestingness? Then there will be two kinds of circles, outgoing and incoming. Will they be there? Double the number of dimensions?
2. Circles tend to produce more circles. Wherever there are overlapping circles there will be unions, intersections, differences, products etc. It's the basics of the Set Theory. Examples? Well, union is the simplest, and it's already implemented in Google+. Just check as many circles as you want when you're sharing something - that will be a union. Intersection? Let's say I have "Geeks" and "Can read Russian" circles. When I post something geeky in Russian, guess who would I like to address the post? I believe the intersection of "Geeks" and "Can read Russian" should be my target. Next the difference. Let's say in addition to the previous two I also have "Coworkers" circle. Again, all of these three circles can overlap easily. What if I want to subtract "Coworkers" (including my geeky boss) from "Geeks" circle if I'm going to ask an advice on, let's say, job hunting from all my geeky friends? So there should be a subtraction functionality in G+ circles too. I hope Google will think about all this math.
So there is plenty of work to do to implement the circles properly. The only hope is that Google has enough resources to do it right. Maybe it's not time yet, and that's why the enrollment to G+ is limited for now. For the meantime Google+ is just raw. Well, no problem, we can wait.