I find both Facebook's groups and the Ning sites are less than usable for my needs. Both are far too complex for effective occasional use.
This is a general criticism of community web sites. (And not a criticism of the importance of the community or it having a site.) It is also another data point in the discussion about primary and secondary awareness and information tools. For the community organizer the community's site is a tool for doing stuff. For the community member the community's site is for awareness about stuff. While community site's tools and presentation need to support the organizer and members it should foremost support the members.
Primary tools can be complex because their use is a significant part of our getting things done. A good example of primary tools are email clients and spreadsheets. Secondary tools need to provide only what is necessary to raise our awareness or get a specific task done quickly and without or with minimal training. Anything more and the secondary tool is competing with the primary tool. And when it competes it looses.
For any community web site, all an occasional user needs is a single page -- preferably the front page -- with the following four sections
1) the next few weeks of events (and an iCalendar feed),
2) announcements (and an RSS feed),
3) news highlights (and an RSS feed), and
4) a welcome section for newcomers.
Any more structure, information, or functions than that and I am lost, overloaded, and/or distracted. And if this is my response, then I suspect it is the response of the other occasional users.
If there is a way for getting this kind of presentation in Facebook groups and Ning site please tell me. Otherwise, I just need to keep myself organized -- which is not a bad thing!