Here is a researcher pointing out that social media is just another outlet and your "presentation of self" in the new media is just like every other aspect of yourself, i.e. you are what you are and people can quickly identify what kind of person you are. With social media you can't control the impression you give people. With the omnipresence of social media and the kinds of digital clues of what you are about means that you can no longer "control" your presentation of your image.
I find the discussion around 4:00 into the video the most fascinating. The idea that when we lived in small communities we were "just ourselves" but as we moved into mass society we were anonymous but with the ability to control our "presentation" of self. But now with the new social media, we have lost control of the ability to manage the presentation so we are returning back to the small community world of just being ourselves.
Here's the Wikipedia write up of what Sam Gosling, the professor of psychology at UT Austin is stating in the above video clip: "The question of whether social-networking sites lead to accurate first-impressions has inspired Sam Gosling of the University of Texas at Austin and David Evans formerly of Classmates.com to launch an ambitious project to measure the accuracy of first-impressions worldwide (YouJustGetMe.com)."