This is a great post by Ben Yoskovitz. He says that even business blogs are personal because you're communicating with someone. Or, as he puts it "blogs are ultimately conversations."
At least that's what we hope they are. Until we can pull a prospect into a conversation (or a partner or employee or current customer, for that matter), we can't really do any business with them. We need that conversation to put another brick in the bridge between us that will ultimately be our relationship. When we have that, we'll be doing business.
The biggest mistake you can make with a business blog, in my opinion, is creating the content in strict accordance with your accepted and approved corporate communications guidelines. You may as well print it into a brochure. More people will read it.
If you have someone in your company that can speak freely and honsestly with your audience, launch a blog today. If you're not willing to have honest conversations with people, skip it.