Let's look at a few articles to explore what these people mean by "structured blogging".
Structured Blogging: Who is Benefitting and How? ... "an initiative to add structure to blog posts of similar content". An example given is if several authors post reviews of the same object, it would be helpful to aggregate those reviews together. But today it's manual because the review format is wildly different between reviewers.
StructuredBlogging and the Classifieds Market: Discusses how this could be used for "classifieds advertisements". Presumably a site like craigslist could be built by aggregating classifieds ads rather than having users post their ads to the central site.
Structured Blogging Initiative home page: "Structured Blogging is a way to get more information on the web in a way that's more usable. You can enter information in this form and it'll get published on your blog like a normal entry, but it will also be published in a machine-readable format so that other services can read and understand it."
Microformats Primer: This idea is just an application of another buzzword that's been floating around, namely "microformats". A "microformat" is said to be a simple data format which conveys data useful to humans.
I think that gives us enough to chew on here ...
Again, let me say this looks to be an overhyping of an obvious idea. For years we've been developing XML as an open data format. XML is the basis of these initiatives they're talking about. For years the paradigm has been under development to separate data from presentation. Hence, we have CSS to handle the presentation and XML to handle storing data.
Clearly, as these people say, it's helpful to have agreements on what XML tags to use in structuring your data. To take the classifieds ads example, if one site uses a TITLE tag for the ad title, and another uses a NAME tag for the ad title, then the third site that tries to aggregate those two has a problem on their hands.
So I applaud the attempt I see at the structured blogging site to normalize the data storage. At the same time I think they're overhyping this.
Further calling it "structured blogging" is silly. This should apply to every kind of web site. In case it's not obvious a blog is just a web site, and there's nothing special about sites that are organized as blogs. Hence the initiative they're pushing shouldn't be limited to blogs, but should apply to all web sites.