As I'm sure you've seen with the Kony craze, one of Facebook's marketing advantages is that content can sometimes go viral, which results in significantly higher exposure. The more people that engage with your content (Likes, comments, and Shares) in relation to how many unique people have seen it, determines a Page post's virality.
The Facebook Help Center summarizes virality as follows:
How is Virality defined for each of my Page posts?
Virality is the number of people who have created a story from your post as a percentage of the number of people who have seen it.
A recent Quora question about virality received an excellent answer by the company EdgeRank Checker, which specializes in studying Facebook's EdgeRank algorithm. Here's the query:
What is an average virality rate for Facebook Page posts?
Facebook Insights gives page owners a rate of virality (the percentage of people who created a story from a post out of the total people who saw it). What is the average rate of virality for Facebook pages? What is a strong virality rate?
Here's the answer (refer to the chart above):
The median Virality rate for Facebook Pages is 1.92%.
I thought this was a great question and decided to do the research. A strong virality rate seems to be +2.5% compared to the typical Facebook Page. We analyzed over 10,000 Pages during the time frame of 2/3/12 – 3/3/12 with over 375,000 individual posts. Page Size and Post Frequency varied from Page to Page.
Wait a minute, average and median are not the same thing! "We know," EdgeRank Checker Founder Chad Wittman said in a statement. "The question came in on Quora asking for the average, but we feel that the median is more accurate. The average was technically 2.97 percent, but that is an average of an average."