Do something useful: free sotware + activism (Score 1)

Challenges? There are many challenges out there, but maybe not in the typical businesses. I would personally advise you to look first at the project that would motivate the most and only later about ways of gaining money doing such. There are a few zillions of free software projects where you would "work for someone else", but together with a community of other motivated developers, facing challenges, solving problems and finding creative solutions. Moreover, with the last boom of the Occupy movement (and the revolutions against dictators in the Arab world), there are many more interesting projects with amazing challenges out there. My bet is that building decentralized tools for activists wraps the next big technical challenges (personally I'm helping in comunes.org). Helping to solve them is not only very self-satisfying, but is being certainly useful for our societies. Moreover, creative solutions might be game-changers in many fields.