People will contribute their brainpower, but only if they're given an enjoyable, time-killing experience in exchange. Play is the unexpected glue that lashes human brains together into a global overmind. So to build a good human-computation project, you can't merely be a scientist; you also need to be a videogame designer.
This, as it turns out, is a significant hurdle, because few academics are trained in game design.
The author is the excellent Clive Thompson.