I do often (but not always) remember people that have the same theme for a very long time (or always have the same character) by that theme, kind of like having a face to put a name to. It really depends on the individual whether I actually picture them as that character or not, though. In most other cases I don't picture people at all. I've never been in the post-a-pic thread so I dunno what anyone looks like.
I won't judge a person because of their theme unless it's just so disjointed, messy, or cluttered up with junk that it gives an impression that the person is, too, especially if the actual content of their posts confirm this. I really don't see that too often at all, though. I might also judge if a theme gives off enough of a pretentious vibe, but only if I'm in a sour, resentful mood to begin with. Again, if the content of their posts don't back it up, it goes away.