Yes and no, when I see comments on my review from someone I have had run ins with before I try to at least read a few of theirs and review. With so many reviews, people, followers, people I am following, it's impossible to read all the reviews. So I just randomly check them out from time to time.
I don't really keep up with which reviewer has commented on my reviews. I've read far many more than I've written, so I imagine I've gotten around to commenting on one or more reviews of most everyone who has commented on mine. But I don't feel a need for doing it, no.
No, not always, though if someone leaves me a really detailed and thoughtful comment on a review I will at least try and respond to it and maybe will go out of my way to make a comment on one of their reviews.
I respond to comments on my reviews, and I reply on people's walls, but for the most part I don't end up commenting on other people's reviews of the same products unless I had already been planning on reading them.