I'm not sure the idea is to build a viable business. Rather to build out an application, and practice creating. We did the original rails day, the precursor to

I'm not sure the idea is to build a viable business. Rather to build out an application, and practice creating. We did the original rails day, the precursor to rails rumble, at Odeo. Then a while later we got the idea of doing that within the whole company, during the day. That lead to a series of hackdays, which created twitter. Seems like, despite it's detractors, to have evolved in to a viable business.