Having been the guy creating the powerpoints to spoonfeed to the board for a fortune 500 company, I'm going to say in the large public companies the C level people try and keep the board as far away from constructive input. Being the guy who has pointed out that something may be deeply flawed let me tell you this is not a good way to advance your career.
Of course, that is how the majority (if not practically all) of boards work. I'm just suggesting that it SHOULD be the role of a board to provide constructive feedback to management, especially when things are not going well.
As it stands, most boards are simply the representation of investor interests, quite divorced from company and management interests, which just makes the problem of getting help when things are not going well even worse. Without a functional inside team providing constructive criticism or a functional outside team providing advice and constructive feedback, then it's difficult for companies of any size to get any realistic feedback at all.
It takes a powerful, charismatic CEO who both the board and employees respect in order for critical and dissenting views to be delivered without someone's head getting cut off. (basically, Steve Jobs and a scant few others).
