Where is geothermal being used most?

The vast majority of geothermal power is produced and used in California.

http://www.nrdc.org/energy/renewables/geothermal.asp

http://www.smartplanet.com/blog/intelligent-energy/google-project-maps-us-geothe
rmal-energy-potential/9934

http://geothermal.marin.org/geopresentation/sld115.htm

4.