I think interlocks are more common than you may think, and I disagree about the impact it can and does have.
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](http://www.usatoday.com/money/companies/management/2002-11-24-interlock_x.htm)
[
](http://www.usatoday.com/money/companies/management/2002-11-24-interlock_x.htm)
According to a 2003 article by Noah Wardrip-Fruin and Nick Montfort which appeared in New Media Reader
The wikipedia article where I found that quote also contains graphs showing interlocks from as recently as 2004 which make it clear that “friend of a friend” relationships are pervasive in both business and government. The 2010 documentary movie Inside Job also shows how the banking industry and government regulators are interlocked with each other, to the detriment of the economy.
Further, interlocks occur not only between businesses, but also in the form of boards of non-profit policy groups, which are not regulated by either the Clayton Act or it’s predecessor, the Sherman Anti-Trust Act.
Also, the Clayton act only regulates businesses in the United States. Multinational and transnational companies escape it’s reach.
Here’s a graph showing the CFR’s interlocks, in case anyone is curious.