Warren E. Buffet is well credentialed to comment on boards, having served as a director of 21 publicly-owned companies over the last 62 years. In his letter to Berkshire shareholders, Warren talks about the changing landscape as we see women slowly attaining status in the boardroom, but he notes that it's still a work in progress.
He also talks about the "bedrock challenge for directors" being to find and retain a talented CEO with integrity, and the importance of in-camera boards sessions to frankly discuss CEO performance.
He discusses the issue of director independence, citing the example of non wealthy directors (which he gives the acronym NWD), noting that perhaps they don't seriously challenge their CEO, in the hope that they will be recommended for a second board position by their CEO, in order to be paid a second set of substantial director fees.
He says that at Berkshire they "will continue to seek owner-orientated directors" and alludes to the fact that he checks the shareholdings of companies to see if its directors have in fact purchased shares of the company with their own money.
Read Warren Buffet's shareholder letter here (his review of Boards starts on page 12 of his letter).