American Society of Civil Engineers:
The U.S. generation and transmission system is at a critical point requiring substantial investment in new generation, investment to improve efficiencies in existing generation, and investment in transmission and distribution systems. The transmission and distribution system has become congested because growth in electricity demand and investment in new generation facilities have not been matched by investment in new transmission facilities. This congestion virtually prohibits outages required for proper maintenance and can lead to system wide failures in the event of unplanned outages. Electricity demand has increased by about 25% since 1990 while construction of transmission facilities decreased by about 30 percent.
The Helios Conspiracy touched on some of this, but the problem is far greater than most of us are willing to imagine, even in fiction.