There are approximately 50,000 geothermal heat pumps installed in the United States each year.

U.S. Dept of Energy reports there are many benefits to geothermal heating systems. Because GHP systems have relatively few moving parts, and because those parts are sheltered inside a building, they are durable and highly reliable. The underground piping often carries warranties of 25–50 years, and the heat pumps often last 20 years or more.

http://www.energysavers.gov/your_home/space_heating_cooling/index.cfm/mytopic=12660