A blog from the CEO of a major corporation can have some major media benefits, but it's also important to consider the possible risks. The main thing to consider is that a CEO blog effectively turns the CEO into the company's public spokesman. This seems fine for charismatic, down-to-earth CEOs (imagine if Frank Perdue in his heyday had been able to blog about his chickens), but not everyone who has the skills to climb the corporate ladder has that sort of personality. Even for those who do, there are long-term image risks.
CEOs don't live forever, and in today's business environment, a company should consider itself lucky if a CEO even lasts long enough for old age to be what causes him to leave. The point is, CEOs come and CEOs go, but you want your company's image to be permanent. What happens when consumers and investors get to know and trust a CEO's blog, only to discover he's guilty of fraud, or involved in a social scandal, or simply leaving the company for whatever reason?
In short, various executive boards, if you're going to let your CEO out onto the internet, make sure you have a contingency plan.