I usually always reply to comments. Even comments that just say a simple "thanks for the fav!" Because I hate being totally ignored. Especially if that person isn't famous at all. But if they are, I understand why they don't.
I like replying to people when I can, but only if I actually have something to say. I hate sending just a "thx" because when people do it to me, I feel like they just did it because the feel obligated to be nice. when I comment, I feel like if someone wants to read it and they like it, Ok. but if they don't I don't really care. I guess i'm just used to being ignored though. I do read every comment, fav, and everything else I get. just because I don't reply doesn't mean I don't care.