On the subject of comments, I too have a problem with replying to other people's comments on cards I have made. Is there an easier way to comment? Not all screens on this site have the same "reply" options and you can't sent a message to someone who is not your "friend".
When someone comments on a card, it will say " (So and so) commented on (my names's) card." Click on that person's (So and so's) name and it should take you to her page where you can leave a comment thanking her for commenting.
Unfortunately Stamp TV is a "Ning" website so there is not a way to just tie it in with blog hopping. You can sign up for a free account using Google's G-mail and then it's much simpler to comment on blog hops. But there will always be some that aren't tied to any kind of account.