Around the world their are people taking part in hack days, it’s always inspiring to hear about what gets built. Here are some stories from the wild:

Guardian Hack Day: The presentations
An archive of a live blog from a 2 day hack day at the Guardian.
http://www.guardian.co.uk/info/developer-blog/2012/feb/03/guardian-hack-day-2

The Hackathon Is On: Pitching and Programming the Next Killer App
Bleary engineers run on little sleep, free pizza, and series-A dreams. The goal: to build a company in two days.
http://www.wired.com/magazine/2012/02/ff_hackathons/all/1