Groups are a great thing. Groups give a sense of belonging. Groups are a reference point for getting recommendations and assistance.
Different social networks seem to have different group paradigms, but the underlying assumption of all the social network "groups" seems to be that there is a leader and then there are joiners. The paradigm also seems to assume that the joiners will come on a "pull" basis to check out what is happening with other group members. This paradigm is vastly inferior to a listserv (think yahoogroups) where anyone can post to a group. In fact, it's even inferior to blogs, which I can at least get in my RSS feed. Yes, the truth is that Facebook and Ning groups suck. Now LinkedIn is following suit. I haven't joined a group there yet, but let's just say I don't have any great expectations.
The one real use of Facebook Groups is to find more friends you know and attach names to faces. So you join a group, let's say the Digital Eve Israel Group. Now you can see the actual faces of all the women you've been e-mailing for over 5 years on the list. You can "friend" them and then you seem really well-connected. Yay! Not.
Now if you join the Tel Aviv Rollers group, that is really useful because you see these guys ever week but for the life of you can't remember their names. Yay! Only they look totally different in their pictures than they do in RL and half the time it's no use. But the other half, Yay! Not.
I mean, it's not totally useless, but it's hardly what I would call a "group" in terms of allowing you to communicate with other members of the group. It's amazing that an application that Yahoo has gotten so right for so long is completely mysterious to the builders of social networks. A group is where you communicate among the group, not an announcement list where only the administrator can send something to the group.
On Yahoo or Google groups, anyone can send a message to the whole group. On Yahoo there is a group calendar, so all events are in one location. As a list member, you are informed when anyone uploads files or pictures to the group. This way, whenever anything happens in the group, you, a member, are notified.
On social networks, the groups are just kind of there. You can post on various boards (discussion, wall, etc.), but you aren't informed when someone posts on the board. So if I have a great event going on in Hod Hasharon, and I want to inform the 1000 members of the FB Hod Hasharon group, I can post there, but most of them don't check the discussion groups regularly, so none of them will know. The only person who can actually send to the whole group is the group administrator.
One of my associates, Sharon Weshler, has a group where he sends out weekly announcements of what is happening on the group. You shouldn't have to do that. Your group should inform you in some way, preferably a configurable way. You could choose to get a weekly update from Ning or Facebook, or you could get on-the-fly updates through your RSS reader.
I've administered and led a lot of groups. No matter what group I've been a part of, virtual or real, the power of the group is in the GROUP, not concentrated in the leader. A great leader is one who delegates and leverages the strengths of the group members. So far, none of the community sites I've seen have put together the right paradigm for allowing great leaders to do this.