28% of American adults use mobile or social location-based services, including mobile maps

"More than a quarter (28%) of all American adults use mobile or social location-based services of some kind. This includes anyone who takes part in one or more of the following activities:
28% of cell owners use phones to get directions or recommendations based on their current location—that works out to 23% of all adults.
A much smaller number (5% of cell owners, equaling 4% of all adults) use their phones to check in to locations using geosocial services such as Foursquare or Gowalla. Smartphone owners are especially likely to use these services on their phones.
9% of internet users set up social media services such as Facebook, Twitter, or LinkedIn so that their location is automatically included in their posts on those services. That works out to 7% of all adults."
Source:  Pew Internet & American Life Project, 6th September 2011