Blogs can be used as great tools for brainstorming. Keeping up with a blog while completing my degree can be a great way to reach out to others in my program. It will be a great way to share best practices that I have found along the way, resources that are helpful, and reach out to other in a time of need. In the professional teaching world it can do the same thing. Instead of reading a "how to" you can read experiences from real life teachers that have gone through or are going through the same things as you are.
Using a blog in the classroom maybe a different story. I have never seen a blog used in the classroom, until now. I feel as though it will be a good tool to have everyone collaborate on an idea. For example everyone reads chapter 1 in the text book. The teacher posts added materials such as video clips and some food for thought questions. Then students can comment accordingly. As the year continues maybe even having each student take the "teacher role" and find added material and pose questions for their peers.