When his blog was active, William Gibson talked a fair bit about mediated personalities - how sometimes he was surprised to encounter the mediated William Gibson, and how different that person was from the self he usually related to.
What we do when we write in our livejournals is creating a mediated personality of our own - we shape how our readers see us when we pick and choose the thoughts and events in our life to write about.
If you ever thought telepathy would solve the world's problems, look at livejournal more closely - when people can read what other people are thinking, what's bugging them, etc., we tend to get Drama. As LJers progress, many of them begin to more heavily censor thier journals to avoid Drama. This tends to mean posting less about intensely personal feelings and experiences, which in turn mediates the personality that readers experience.
The person you all know as
(this may be what happens when I start reading more non-fiction humanities books, and drinking caffeine.)