Whew, I bet that causes some problems for threaded readers: I know when I used to be more active on forums I rarely used the proper reply buttons to compose my posts.
Quite a bit, in fact, from time to time but overall really not so much as you would think if they had a sane quick-reply feature since ultimately people are lazy, if the easiest place to reply is the right one things work a lot better. Pedantically, I'm referring to where clicking reply opens a reply box under that post and maybe with quote so you KNOW you are replying to that, or you use the box at the bottom which joins the main "flat" thread of responses of everyone yelling at each other in a single-threaded dance to the "right".