I've thought a lot about social networks being used simply as next-generation forums.  I believe there is no evolutionary advancement as a web communication tool if a social network tries to meet the same community dynamic as a forum. 

There are essentially 4 categories of group communication:

1. Mailing lists / Bulletins
2. Forums / BBS
   
3. Blogs
4. Social networking 

The first 2 are really "one-to-many" broadcasting tools.  And the last 2 really fit into the "many-to-many" framework.

There is an excellent article from gospelcom.net that addresses the first 2 tools.  And it hasn't gotten the attention/links it deserves.

A discussion list containing more than about 200 people can generate so much discussion that its size will be self-limiting because people will leave when the email load becomes too great. On the other hand, bulletin boards do not usually generate significant discussion until site visitors reach about 2000 a day.

This tip alone would have saved these churches from creating message boards for their own church communities.

BTW, every word in the above sentence is a link to a different church forum that has little to no usage.  Yes I'm good at teh google (or I have too much time on my hands).

The only successul church forum I've seen is McLean Bible Church, which has 4000 members registered to its forum.  Like GospelCom says, a threshold of 2,000 is needed for a forum to survive.  One-to-many communication tools need the "many" part to function properly.  

So if a church has more than 200 people online but less than 2000, what tool serves them best?  I believe the many-to-many tools of social networking and blogging is a right solution (not "the" solution, but "a" solution - as Seth Godin would point out)

And I am certainly not arguing that social networking is the silver bullet that will solve a church's communication needs.  I don't think a private social network will survive for a typical-size church.  It may go the way of the dodo bird church forum.  And the same web design companies that sold churches the forum and bulletin board software for the past 3 years, will try to sell them social networking software for the next 3 years.  (I'm already compiling a list of companies jumping into the social networking game that I will reserve for a future post)

Social networking has a threshold too.  Time will tell what that threshold is...  Think of this: if Facebook never expanded past Harvard, would it have survived?  Possibly (Harvard is a pretty big place).  But because it expanded and scaled its scope of network effects, the ratio of min-threshold to potential userbase tipped the scales in their favor.