I find that I regularly check Facebook and am regularly disappointed with what I encounter there both as it relates to the activities of my friends and their responses to my activities. I tend to want deeper feedback and discussion which clearly isn't the model for Facebook. Whereas I know plenty of extrovert friends who love Facebook, are constantly checking in and because they have hundreds of friends, are constantly validated.
Certainly this is all anecdotal and biased given that I'm strongly introverted but every time I see someone say they are giving up Facebook or are disappointed in it (including myself), it seems to me that person is most likely introverted and thus not well served by the end goals of Facebook.