BBC News this afternoon looked at the public suggestions for sealing the BP oil well as an example of crowdsourcing. It includes a quote from Crowdsourcing author Jeff Howe on why crowdsourcing is sometimes essential:
But one time out of a hundred the problem seems intractable. Crowdsourcing has revealed — in those intractable cases — you need someone who is not trained. All the steps the experts have thought to do haven't worked. You need the unexpected.