If someone is nice enough to comment on your blog, respond. There is nothing worse then an unresponsive blogger, especially a larger blogger. It gives the impression of a blogger that is not plugged into their own network. The responsibilities of larger blogs do tend to throw more things on the plate and interaction between the community changes, but a comment on your own blog is the cherry topping. Answer, even if it is just a Thank You and then maybe respond with a return question to keep a conversation going. The goal is to have a forum type setting and your posts to become go-to spots for information and conversation. This will increase pageviews and grow a loyal following.