I just suffered the horrible collision between worlds that keeps many people out of social networking altogether. You can read about it in older posts here.
What the Social Networking model lacks, even with Google+'s innovative circle model, is passive decay of connectedness strength. That is, what the social networking model fails to reflect is that social connections become less relevant over time if the interactions between the people are infrequent.
Even simpler, people lose touch.
We act like we never want this to happen, it is something of a standard declaration of the intensity of a bond to say that "we will never lose touch!" Sometimes it is true, but not always. Some times you do lose touch, and that connection becomes less socially relevant as time passes.
I have important people in my life whom I have known since I was first aware of other people who remain important to this day. However, I have had recent contact with each of those people--that's what makes them important now.
I remember people from my early childhood who were vitally important to me then but who I no longer know if they remain alive. Probably many aren't.
I have had very important people in my life, people I love dearly to this day, people who would be welcome in my life at any time, with whom I have not had any direct communication in many years. These are people who shaped me into to who I am today, people whom I cannot imagine what my life would be like today without them having been in it.
I don't care if they are "Having a busy Monday" (to borrow a rant from a recent article making the rounds on Google+).
I have very important people in my life whom I have know for less than a year, people with whom I am bonded professionally, whose welfare is a central concern of mine, and I do very much care that they are "Having a busy Monday." However, if I were to change jobs, my interest in them would quickly be extinguished, despite the fact that they are decent human beings who are worthy of such concern.
Google could mine this information from my GMail. They could figure out who I am in frequent e-mail communication with and elevate those people's presence in my stream. That would be useful.
Conversely, they could quiet the posts of those whom, while I do know their e-mail address, I never email.
That's more like what my actually social life is like.