The U.S. Service Sector is not only the economy's most diverse sector, it is huge - employing 90% of the workforce. Service workers are the highest paid and best educated, and they are the lowest paid and least educated. The sector encompasses neurosurgeons, college professors, delivery-truck drivers and dishwashers.
The United States Census Bureau published an interesting study entitled "1940-2010: How Has America Changed?" Looking at the American workforce, we see that it has more than tripled in the last 70 years with a major industry shift from jobs in manufacturing and agriculture (41.9%) to service jobs. This mega trend is unlikely to reverse any time soon.
Recent data from the U.S. Bureau of Labor Statistics supports that services is the fastest growing sector of the U.S. economy. Look at the infographic produced by the International Businesss Times where service related sectors are where the growth is (blue).