The hype around blogs has had an interesting effect on the perception of message boards. This post from Common Craft takes an amusing look at the rise of blogs in comparison with message boards. The takeaway (regardless of whether or not you agree with conclusion) is that community is key. Blogs have an open but loosely coupled community, message boards have a closed but explicit community. The point of the post is that different communities enable different visibility and the potential for different focus vs breadth.
I'm not sure I agree with much of the post. For example, message boards can be very personal as well as highly focused - the same goes for blogs. One of the aspects of both of these publishing mechanisms that is often ignored is that the mechanism itself - the platform - is just a syntactic structure. The needs of the participants or authors will find expression somehow through that structure.