When I'm reading a comment written by a name that I've seen enough to associate a personality with, I'm almost always aware of whose comment it is. But, when it's not a name I know well, I'm not consciously aware of having looked at the name and made that determination. So I think I must always read the name, and if my brain doesn't recognize it, it automatically filters it out.

On LW, I hardly ever notice the username. (I tend to notice more often on sites where people have avatars, and sites where I know most of the people whose comments I see.) I think I might be skimming the names, because I remember noticing usernames of people who I already knew about, but can't remember actually reading and comprehending usernames I don't recognize, at least not very often.