Crowdsourcing is meant to tap into the power of the Wisdom of the Crowds. But does it work? The wisdom of crowds is meant to tap into the power many people arriving at a better answer than any one individual. Crowdsourcing does this via various Internet means.
The critique of crowdsourcing is that it is too highly influenced by public opinion, similar to groupthink. (An article in the December 2009 issue of Communications of the ACM discusses this point, and the Wikipedia page on The Wisdom of the Crowds has a similar argument.)
Looked at from another angle, crowdsourcing suffers from participants having uninformed opinions. The wisdom of crowds works when everyone is making educated guesses. Crowdsourcing breaks down to an uninformed mob. Conversely crowdsourcing should work when the target crowd is fairly knowledgeable.
Leo Laporte's TWiP podcast has chat rooms filled with fans during the live podcast. This group tends to know quite a bit about technology and so "crowdsourced" questions to them result in nice answers. Good. But then digging through product review forums on random websites shows quite a number of people yammering on about products they don't own and giving lame and often incorrect generalizations to questions. Bad.