Anyone who thinks that all their facebook friends are "real" friends hasn't thought too hard about it.

as for,
You can tell it "more about so & so vs. less about so & so"
They changed that about two weeks ago. You can either hide people or not, there's no inbetween. I have quite a few people hidden as I have no interest in what they post or how often they post it, but I can go look if I want.

I use it to BS with people that I really mostly, and keep it pretty non-intimate. To do otherwise is pretty stupid, but then again people get pretty stupid about internet behaviors. This is nothing new.

I have unfriended people from a past life who contacted me and then I decided I just didn't need those connections. They don't know if you unfriend them; at least they don't get notified.

Part of the reason is that as a future therapist, I don't want my clients knowing about my personal life.
You can set your permissions so that only certain people can see your full (or professional) profile