Science Daily reported a study led by Sam Gosling at the University of Texas at Austin that examined whether people's Facebook personalities present a genuine, accurate view of themselves, or whether people tend to embellish and manage impressions of themselves by projecting an idealized virtual identity.
The study involved 133 Facebook profiles. Participants were students at the University of Texas at Austin. Participants were broken into groups of 5 people who knew each other. To determine actual personalities, they each completed a Ten-Item Personality Inventory, which rates the Big Five personality traits, about themselves and each of their four friends. The survey also measured each person's "ideal" self - how they wished to be. To make certain that Facebook profiles weren't altered, researchers saved the profiles prior to informing the participants about the nature of the study. Nine undergraduate research assistants who did not know the participants independently rated the personality traits of the 133 based strictly on their Facebook profile. The research assistant's assessments were then compared to the self- and acquaintance reports of the participants, each rated equally. The results? While the researchers expected to discover that the Facebook profiles matched the idealized version of the participant's personality, there was agreement that the profile actually communicated the real personality. This held particularly true for the traits of extraversion, conscientiousness, and openness to experience. Consensus for agreeableness and neuroticism was weaker. Gosling notes that neuroticism is hard to identify without face-to-face interaction.
The researchers aren't sure whether people are just being themselves on Facebook, or whether they're trying to seem idealized and just not succeeding.
The gender and ethnic backgrounds of the study participants were diverse. It would have been interesting to see a broader range of ages. In particular, I'm curious as to whether older people would have shown the same results. Based on this study, it appears that people - at least college-aged students - project accurate views of their personalities and are using Facebook for genuine social interaction. It seems plausible to me that offline personality would mirror online Facebook personality. For something like an online dating site, one would probably try to convey an impression of their more "idealized" self, because these people don't know you in real life. But many of your connections on a Facebook site are friends who already know the real you. There's less incentive there to make false claims or exaggerate, because you'd be called on it.
Here is a video clip of Gosling discussing the study.