The comments issue is why I typically reply to list comments I receive on the profile page for whoever commented. It would indeed be nice, however, if there was a way that we could be alerted when someone replies to a list comment that we have left. Just please don't let it be a "somebody commented on a list you commented on" thing, as I don't need to see every last comment on every list I've commented on. ;)
Funny, this subject came up earlier today between myself and Trebek
I too would be down for the idea of seeing icons next to lists I've left comments on, but I think we'd need that in addition to the alerts for reply comments.