I usually mark as read when I read them so my new mail indicator is cleared. Some replies/comments require jumping around other posts/comments or doing some research in other tabs. Also (unrelated issue), I don't know if others have this issue but the green band to the left of new replies/comments does not display well on my Kindle, it can be hard determining whether it is new or read depending on the magnification of my screen. I have to look at the "mark as read" text and timer to determine if they are new or old. I go back to my POAL tab after being in other tabs and I sometimes get flooded by more replies/comments and lose track of those I meant to respond to but was distracted earlier. A small flag indicating whether I've replied or not would not effect the new mail indicator function. I use saved replies/comments for particularly informative comments or posts I wish to save.