I think writing comments is always is very special thing and even more important than post, because this is a communication and not a monologue of author. For me it depends on my mood and been tired or distracted by other stuff. Short comments with simple words, yes, I need to confess sometimes I do them too, although try to avoid when possible. I like to write when I want to but if someone will tell that you have to write comments to as many posts as possible then no, I will have an inspirational block.