The Wisdom of Crowds makes some good points about how and when a large number of people can do things better than experts. Crowdsourcing often refers to splitting work across a large number of people. However, what I occasionally see is a "crowd-based" problem-solving approach which is... not really.
For example, if you have a difficult problem, you might shove it out to the crowd. A fan of crowds might say the Netflix Prize was solved that way. However, in that sort of case, it isn't the crowd solving it, it's some bright people. You've just given the problem to some bright people, and a bunch of normal people.
In other words, crowd-sourcing like this is not really about problem-solving, it's about problem-routing - effectively packet-switching problems towards the appropriate experts, even if you don't know who they are. You feed the problem into the social graph and hope it is forwarded to an appropriate destination.
Sometimes, a crowd really is only as wise as its wisest members, but in a large crowd that can still be pretty darn wise.