From the National Air Traffic Controllers Association FAQ we can see some interesting numbers.
On any given day, more than 87,000 flights are in the skies in the United States. Only one-third are commercial carriers, like American, United or Southwest. On an average day, air traffic controllers handle 28,537 commercial flights (major and regional airlines), 27,178 general aviation flights (private planes), 24,548 air taxi flights (planes for hire), 5,260 military flights and 2,148 air cargo flights (Federal Express, UPS, etc.). At any given moment, roughly 5,000 planes are in the skies above the United States. In one year, controllers handle an average of 64 million takeoffs and landings. ...
There are 14,305 air traffic controllers that work for the Federal Aviation Administration, according to FAA data (dated Aug. 2006).
Assuming the air traffic controllers don't work much overtime (unlikely) we can guess that 20% of the ATCs may be on-duty at any particular moment -- they work 24 hours a day, seven days a week -- so about 3,000. Does it really take 3,000 air traffic controllers to coordinate 5,000 flights?
I'm not a pilot, so am I missing something? Is our air traffic management system so inefficient that we need a controller for almost every flight?