BusinessWeek wrote an article about Social Networking with the Elite yesterday that focuses on Social Networks that are meant to be invite only like INMOBILE.ORG:

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INMOBILE.ORG

 

Launched in April, 2006, INmobile.org is a network of more than 900 executives who work in or close to the wireless industry. To qualify, you have to be at least a director at a large company, a vice-president at a mid-size company, or in the C-suite of a startup. So far, members include executives from carriers such as Verizon Wireless, content providers such as Walt Disney (DIS), and handset makers such as Nokia (NOK). Arthur Goikhman and Stephen Dacek, co-founders of New York mobile-games startup Cellufun, joined in February. They were able to make connections with Yahoo! (YHOO) on the site and struck a deal with the search giant to place ads with Cellufun's games. "I'm glad it's not a free-for-all," says Dacek. "It really does make it a lot easier to network."

I think closed social networks can make sense - I use a closed social network for my own Social Media Committee at the Web Analytics Association - only committee members are invited.   In the same way, we initially planned to build the new Web Analytics Association network as a closed social network just for WAA Members - but ended up settling on a semi closed model instead.

It turns out that building a Closed Social Network is actually not that easy to do - most social networks are built to be viral, to expand, to be easy to join - and making a closed social network is actually much harder than leaving it open.

One way to sorta make it closed it hide the signup form on a social network - and then just send invites - but if the social network is crawled by search engines - it will be hard to make a social network totally closed.