Threading like that would be exquisite. As it stands, I have to do the threading mentally and only pull up the threaded view when there's an ambiguity as to who is addressing whom. One nice touch for linear view would be something along the lines of "re: Poster X" so threaded view wouldn't have to be accessed for that information. (I got used to that on UBBthreads, which in every other way sucks compared to this board software.)

edit: I just thought of another nice feature that vBulletin uses: make edits within, say, the first minute not put the 'edited' line on the post. That way, doing things like correcting a grammatical mistake that slipped through preview wouldn't tag on another line to the post.