Predictably, the recent regulatory development in corporate law, such as Sarbanes-Oxley (see my article The Creeping Federalization of Corporate Law) and new stock exchange corporate governance listing standards (see my article A Critique of the NYSE's Director Independence Listing Standards) are affecting the demographics of corporate boards of directors. The Transformation of US Corporate Boards: 1997-2003 finds:
During that period boards become smaller and more independent, there are fewer cases of interlocking directorships and a decrease in multiple directorships. We also find changes in director background: an increase in the number of directors with financial background and a decrease in the number of directors with industrial background. ... We find little change in the financial stake of independent directors and in separating CEOs from the chairman position.
Don't assume these changes are an unalloyed good until you've read my articles cited above.