Have you ever been to an event like the county fair? You look around and see "everyone" carrying bright pink bags. You're not even sure what's in the bag, but everyone has one, so you want one too?
As you come around the corner, sure enough, there's a crowd gathered in front of a vendor, and he's putting his product in bright pink bags. So, you stay and listen to his sales pitch.
What you have just witnessed is social proof, the phenomenon whereby people will look to the actions of others to determine the correct behavior for a given situation. (cite: http://en.wikipedia.org/wiki/Social_proof)
The term was popularized by the author Robert Cialdini in his book Influence: The Psychology of Persuasion (ISBN 0-688-12816-5) which has also been published as a textbook under the title Influence: Science and Practice (ISBN 0-321-01147-3). Check out Amazon.com for reader reviews as another type of social proof.
Social Proof on the web takes a slight broader definition. It's basically people validating your content in some way. Think Digg, or +1, or like.
We see social proof all over the web and on many popular websites. Some examples of social proof include posting subscriber counts, twitter followers, comment counts on individual posts, and even "badges" for the organizations you belong to.
Anytime you can display or seek out social proof, you should take advantage of it. Do you write your content to solicit responses? Do you go back into your comments and start a dialogue?
While the positive aspects of social proof are a plus for your website, be careful of the potential downside. Displaying a banner that says "27 followers on Twitter" might give you the exact opposite response you want.
Some things you might want to add to your marketing campaigns for social proof include social bookmarking, comments, Twitter, and or a Facebook presence.
What say you? What social proof methods do you employ?