Where's Waldo? Where's Wanda? Where's Walter? Finding People with Mobile Devices

"As of August, only 4 percent of American adults who used the Internet also used location-based services, which allow people to “check in” to physical locations via their cellphones to earn coupons or keep up with friends, the Pew Research Center’s Internet and American Life Project reported last week," writes New York Times reporter Joshua Brustein. "And only 1 percent of Internet users are on such services on any given day, an indication that those who do use the services still have not integrated them into their daily lives." The question is why? Do they know about the services? If yes, then is it a privacy issue?