"The bigger your crowd doesn’t necessarily mean better output when it comes to crowdsourcing. This has been made apparent with the early days of crowdsourcing design sites. A design contest yielding 1,000 designs can become simply unmanageable. If you offer a prize large enough, any monkey with a crayon could contribute. I’m not saying a large crowd produces bad results, I’m simply stating there will be bad among the good. Luckily, there are almost always a lot of great designs, but it takes extra time to sift out the bad.
Sites like Genius Rocket have begun shifting to a curated crowd model. Anyone can request to join their crowd, however, they must prove they’re talented before being able to participate in some projects, or even at all. LogoTournament has been silently curating their crowd since the early days." (http://www.businessesgrow.com/2011/08/31/the-top-five-crowdsourcing-mega-trends/)