I think you misinterpreted the parent post. It's saying not saying that Facebook Groups is the same as Google Circles, it is saying that both Facebook and Google+ have the group functionality (in the sense of Unix groups - ie, grouping users for access restriction purposes).
@nl: I thought he was talking about user lists at first too, but he kept talking about groups, so I tried addressing both. You can see it in my reply.
But just to be sure, I had attempted to use user lists in the same way to restrict posting out and I was not able to.
Further, I reiterate: Google+ does not work like Unix groups. It works like Livejournal friend filters. The groups are relative to whatever you define and it is not global across the entire domain, unlike with Unix groups.
To implement circles/friends list as Unix groups, you would have to introduce the concept of namespaces in which the set of groups is scoped within a namespace. Then you attach individual namespaces for each person. In other words, named sets of named sets. The named sets themselves are not global, even though the members are.
So I just checked again. I see that after I click on -> lock button -> drop-down customize -> Specific People and then type in the list, I can restrict the update there.
I am testing this now: Once I select it, it says "Custom Setting saved" ?? Wait, does that mean I can only have ONE custom setting?
I just posted a test post. The resulting post has no indications that it is a special-restricted post. Along with the customized setting, does that mean that I can set a single default friend's list that I then blurt out to? What if I want to switch around?
If you know of an easier way, I will gladly say, I was wrong about Facebook lacking in the functionality I want.
I've mentioned in other comments here, Google+ defaults to "warren" and Facebook defaults to "plaza". Each can simulate the other with some contortions. That makes this more like a set of Evil Twins (http://www.ribbonfarm.com/2009/09/17/your-evil-twins-and-how...).
Meaning, if you don't get why Google+ is a killer app for me, then you don't really need the functionality it provides like I do. And that's reasonable by me. Whether or not this means that Google+ will "kill" Facebook (I doubt it) or not, I don't really care much about it.
There's a persistent myth that Facebook Group is the same as Google+ Circles.
I don't think that myth exists at all - I've never seen anyone say it until you brought it up. The parent post used the word "groups", but didn't specify they meant "grouping people" as opposed to the Facebook group functionality.
Further, I reiterate: Google+ does not work like Unix groups
Again - no one is claiming that. I used Unix groups as an analogy (because they let you group people together).
In Facebook it is called user lists.