The reader takes the time to comment and leave feedback, so I think the author should take the time to respond to that.

Yeah, exactly. It's, I mean, no one has to do it, but I do think it is the polite thing to do. It seems like a lot of authors respond in kind to the feedback they get, saying a quick thanks to people who take the time to drop a quick "I enjoyed this, thank you!" and longer comments to people who give more detailed feedback. As someone who usually leaves detailed fb, I can't help but enjoy this because it can often lead to more discussion and well, isn't thank kind of the point of livejournal?