Ask HN: Are closed social networks as good as they think they are?

I received an invitation to join chamber.com the other day, which appears to be a cross between LinkedIn (as a professional network) and A Small World (being invite only). Honestly, I am starting to feel a bit of social network fatigue and was wondering if these closed communities are as good as they think they are? Are they really that exclusive and useful or is the 'exclusivity' just for show?

Can anyone give me any insight into them please?