A Facebook user who 'likes' content is likely to have twice as many friends on the site than one who does not

"On average, a Facebook user who “likes” your content has more than double the number of friends than does a typical Facebook user. This could mean the user is more “social” or more influential, but on the other hand, it could mean the user is an attention-seeking narcissist. While it’s fatuous to read too much into that statistic, the number does show that the average “liker” is more active from a social-web standpoint.
An even more interesting stat about the likers is that they click on five times more links to external sites than the typical Facebook user. If clickthroughs are what you’re looking for from your social media strategy, this is good news."

Source:  Data from the Facebook’s Developer Network Insights team, reported by Mashable, 29th September 2010