Blogs are a powerful tool for spontaneous communication and can be used to help provide the two-way relationship building that I've talked about on this blog. The primary ways feedback comes is through commenting and trackbacks. Some bloggers are better than others at watching the comments. I urge bloggers to provide feedback to the commenters to make the communication two-way. Doing this will naturally result in more reader loyalty.
Some people are talking about ways to change blogging to produce real conversations.
My opinion on opening up blogs to all comers: you'll end up with Yet Another Discussion Forum.