Some SL residents are largely in character – Dr. Mason, for example, spins an ongoing saga of great complexity and is so completely in character that his rare exceptions are so noted. (OOC aside: Hey, Doc: our typists are practically neighbors, at least on the global scheme of things!) Similarly, Janus, Countess Carenduna’s butler, has no other persona that we know of, so complete is his devotion to character.
At the other extreme, some draw little distinction between their lives and those of their typists. For example, ISC chat will have people discussing their typists’ children, spouses, unfortunate household accidents, job commitments, beers tasted, and so on – merging the personalities of typist and SL character.
For most people, it seems to me, there’s a distinction between the role and the actor behind the role, although the lines between the two often blur. I think most people are comfortable with roles that are consistent with their underlying personalities. That is, the helpful person does not stop giving advice, the garrulous person does not suddenly become shy, and the populist does not turn into an elitist.
At the same time, this is not to say that the character is the typist. We can amplify positive characteristics and downplay the negative. Perhaps each adopts the role he or she wishes to have. Others choose to explore avenues that are not innate to the creator (perhaps that's wishful thinking, but I shall continue to hold this point of view until proven otherwise): the Gorean role player, the Evil Scientist Bent on World Domination, the Fetishist, and so on. Still, my admittedly limited experience has been that even Evil Scientists turn out to be quite nice when one talks to them. I'm not sure what that proves, but there it is.
I assure you, Gentle Reader, that this does not mean I will start a Twitter account and regale you with what I ate for dinner every evening. Some things are best kept to one's self. Whichever self that may be.