I recently attended a meeting at a client. It was a brainstorming session to begin thinking about the corporate blog they had decided they needed. In addition to myself, there were representatives from a leading marketing and metrics company there.
While I think that (for this enterprise) community building tools could only help the situation, it was startling to me how little of the conversation had to do with building a community. At one point, I pointed to all the whiteboards and said, "Looking around this room, I understand perfectly well why you would want to have a blog - I just have no idea why anyone would ever want to read it."
Opening the content of your internet presence to a community for discussion is a risk. People will say things that spin the conversation in a direction you hadn't planned. You need to accept that risk and respond as clearly and as honestly as possible. The open discussion is the point.
This particular client wanted the blog to solve some PR issues they are having. I think it's the right thing to do. It certainly couldn't hurt... unless they do it wrong. And wrong was the way they were discussing it. Their goal was to shape opinion, to respond quickly to negative press, to head off adverse opinions at the pass.
A blog is not a PR tool (or shouldn't be). It is one of many tools available to give users a voice inside your organization and your organization an ear outside your walls. It's clearly an easier risk for a company with a favorable reputation to undertake, it's a far more important risk for a company with a negative reputation to undertake.
I hope they do it right.