What’s cool? Who can be trusted? Why does one start-up go public, while another, which seems to do the same thing, fizzles? What logic, if any, pertains to where the money flows? These are the anxious questions that pervade Silicon Valley now, I think, more than ever — the vague sense of a frenzied bubble of app-making and an even vaguer dread that what we are making might not be that meaningful.