People exhibit less prejudice when they’re in the presence of a mirror, Dutch researchers have shown. … Mirrors make us more aware of our public appearance, and therefore remind us of the need to fall in line with social norms.
More here. I suspect social networking also makes our lives more "mirrored" – we are more aware of how we appear to others and that others are watching us. Welcome to the transparent society. HT to Tyler.
There is some other and forthcoming research relevant to this.
Vaslou et al. (2007) showed how creating an avatar that looks like you can increase self-awareness.
Some further forthcoming research by others shows how seeing your own picture during online profile construction can make you less willing to stretch the truth in your profile.
Vasalou, A., Joinson, A. N., and Pitt, J. 2007. Constructing my online self: avatars that increase self-focused attention. In Proceedings of the SIGCHI Conference on Human Factors in Computing Systems (San Jose, California, USA, April 28 - May 03, 2007). CHI '07. ACM, New York, NY, 445-448. DOI= http://doi.acm.org/10.1145/...
“People exhibit less prejudice…”
The more accurate phrasing seems to be “people avoid revealing socially unpopular views”.