This upcoming Saturday, in many cities around the world, people will participate in the first ‘Global Open Data Hackathon’ ever. You can read more about the event on the website of the event or join
YOUR NEIGHBOURS in Berlin (sign up, learn more, dates, location etc....)

and as I just learned: in Vienna:  Raum D / quartier21 with Michael F Schreiber (WISDOM) (start 11:00)