I don't see too much application of blogs in the medical field. The only case that I could see blogging being useful in medicine is in research. If a researcher is doing important work and wants to keep the public informed of what is going on, blogging can be a very useful tool.
Here is an article form BusinessWeek.com about how blogs can be used in the businesses. While blogs are mostly thought of as a communication tool for high school kids this article shows that it has an actual application in the real world as well.