When you hear the words "social network" you probably think of Facebook or Twitter. But years before either of those websites - when most of us weren't using the Internet at all - a smaller, stranger community was emerging around something called WheresGeorge.com, a 15-year-old subculture that's dedicated to the $1 bill.

At Kabooz's Bar and Grill at New York's Penn Station, Jennifer Fishinger is covering her table in stacks of ones. There are 500 $1 bills laid out.

At the next table over, David Henry has his stacks of cash in plastic bags. They're paper-clipped $1 bills in groups of 10.

For this group, it's all about the George Washingtons. Their dollars are stamped with messages like "currency tracking project" and "Track me at WheresGeorge.com." The website is the brainchild of Hank Eskin, a former tech consultant.

"I started the website in '98 as just a quirky idea. I didn't expect anything to happen," Eskin says. "I had no idea it would turn into a hobby or create this whole sensation."

It's called Georging. And typical Georgers log in religiously to enter their dollars' serial numbers and ZIP codes before they stamp and spend them. If one gets entered a second time, the Georger gets an email. That's called a "hit."

"As a data set, it is very sexy," says Dirk Brockmann, a theoretical physicist at Northwestern University. He was studying human mobility when a cabinetmaker in Vermont told him about the website.

"I was like, 'Oh wow, this is amazing because it's data that goes down to the ZIP code scale in the U.S.,'" Brockmann says.

By analyzing the Where's George? data, he's tested theories about networks, modeled infectious diseases and mapped the flow of currency in the U.S.

"It turns out that what started as a - in quotes - 'silly game' did some massive science, it was like the first measurement of human mobility on this scale," he says.

To read the complete article, see:Where's George?: The Trail Of $1 Bills Across The U.S.(www.npr.org/2013/03/24/174966382/wheres-george-the-trail
-of-1-bills-across-the-u-s)