I never quote the person I'm responding to if they're the last poster, unless I know that it might take me a while to type out my post. Then I will quote the person so I won't have to go back and do it again, just in case.
However, if someone does manage to get in ahead of me, I will edit my post by inserting a quote. But that's me. Some people just have a different style and as long as they manage to convey who they're talking to in one form or another it's okay by me.
