Our ninth Open Hack Day is underway in New York City -- our first time here on the East Coast. Several hundred hackers have registered for the 24-hour hackathon and will work through the night in teams (or flying solo) to mash up cool new creations based on Yahoo!'s open technology. So far we've seen everything from an app that lets you track topics spiking across various social media tools to a site that gives you restaurant reviews by menu item to a 3D printer that, if all goes well, should be able to print Obama's face in peanut butter on a piece of bread.

We kicked things off this morning with a keynote by New York University professor Clay Shirky, whose book "Here Comes Everybody" examines how Web 2.0 is revolutionizing the social order. He tackled the culture of online communities and what motivates people to participate in them. For example, why have more than 3,311 people built out incredible minutiae about Dr. Who on Wikipedia? Why does a guy build the Taj Mahal out of LEGOs and upload photos to a LEGO community site? What happens when a woman who normally blogs about fashion and her iPhone apps decides to post photos of a military coup?

We grabbed a few minutes with Clay after his talk to expand on his themes. Here's the interview:

Our hackers now have bellies full of hot dogs, nachos, beer, and ice cream bars (nourishing hacker food) and are bedding down for a night of coding. We'll see the fruits of their labor tomorrow afternoon when they each have 90 seconds to dazzle the judges with their wares. They probably won't get much sleep, but we hope there will be Obama sandwiches for all.

Nicki Dugan
Blog Editor