If you look at Surowiecki's requirement for a wise crowd (versus a herd), you'll see that he asserts the requirement of a few things (pulled straight from http://www.wikipedia.org/wiki/Wisdom_of_crowds):
Diversity of opinion:
Each person should have private information even if it's just an eccentric interpretation of the known facts.
Independence:
People's opinions aren't determined by the opinions of those around them.
Decentralization:
People are able to specialize and draw on local knowledge.
Aggregation:
Some mechanism exists for turning private judgments into a collective decision.
I would think that for most sites the first three would be the greatest challenges. The worst part is probably that what's most popular is getting greater exposure, thus making it more popular . . .
Independence: People's opinions aren't determined by the opinions of those around them.
Haven't you ever noticed on Reddit: foo makes a comment, and then foo's comment karma drops to 0. All of a sudden, it goes way down to -3. Then bar makes a positive reply and gets a large karma score, and all of a sudden foo's comment shoots back up to 10 karma or more.
Well, people really are influenced by the opinions of others. If someone's downvoting someone, the majority of people are going to agree that downvoting that someone is a good idea. If a group of people are beating up someone, more people join in and beat up that someone.
Did you hear about the Juneteenth mob that pulled someone out of their car and beat them? Someone thought that was a good idea, and all of a sudden hundreds of people thought that was a good idea.
Diversity of opinion: Each person should have private information even if it's just an eccentric interpretation of the known facts.
Independence: People's opinions aren't determined by the opinions of those around them.
Decentralization: People are able to specialize and draw on local knowledge.
Aggregation: Some mechanism exists for turning private judgments into a collective decision.
I would think that for most sites the first three would be the greatest challenges. The worst part is probably that what's most popular is getting greater exposure, thus making it more popular . . .