4% of online Americans use location-sharing services like Foursquare

"In its first report on the use of “geosocial” or location-based services, the Pew Research Center’s Internet & American Life project finds that 4% of online adults use a service such as Foursquare or Gowalla that allows them to share their location with friends and to find others who are nearby. On any given day, 1% of internet users are using these services.
[...]
Key findings include:
- 7% the adults who go online with their mobile phone use a location-based service.
- 8% of online adults ages 18-29 use location-based services, significantly more than online adults in any other age group.
- 10% of online Hispanics use these services – significantly more than online whites (3%) or online blacks (5%).
- 6% of online men use a location-based service such as Foursquare or Gowalla, compared with 3% of online women."
Source:  Pew Internet & American Life Project, 4th November 2010