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Even if they are not actively tweeting, blogging, or posting on Facebook, Google+, etc., I think all CEOs should get the gist of it all, at the very least. As for them actually using social media, I guess it really depends on how knowledgeable they are, in general, on how each site works and how to not directly or indirectly embarrass themselves (and the company) - i.e. bad grammar.
Anyway, great article! I also posted it on our blog here:
10 months ago on Fortune 500 Executives Aren’t Using Social Media and That’s OK