A potential fifth category is the "link blog" that primarily passes along "quick links" (as some call them) without any deep analysis. Or, perhaps "news blog" would be a more generous category label. I tried to get myself to say these fit within Archive; however, the level of original thought (low for link blog) and long term value (again low) seems to separate them into something else yet.
As I developed this taxonomy, I briefly considered transitional forms between each of the four types of blogs. Ray has inspired me to spell those out in detail.
Links Summaries: Blog postings full of links and news items are more valuable to others than the "cathartic process of relief" offered by Distraction Blogs. They are usually not as valuable as the archives of an expert. The value proposition is less permanent than the tangible value of a product. It does take some expertise to assemble the link summaries or news items, like an editor or a maven. But the content is perishable like the predecessor forms of self indulgence.
Fan club comments: Archive blogs tend to share expertise without the professional growing from all the writing. It's easy to generate posts for the archive because the material has been expressed in other venues previously. An intermediate form of blogging often occurs where the expert's posts get incidental praise and validation or personal remarks: "Great post!", "This helps a lot!" "Welcome back from Mexico!" or "Say hi to your kids for me". These "fan club comments" put the "guru" on a pedestal and look up to him or her. They offer adulation rather than eye-to-eye conversations. They introduce a glimpse of relating, reciprocating and growing interactively without getting into the Conversation type of blog full bore.
On site Blogs: There are US soldiers blogging from inside Iraq. There are political activists blogging from the sites of demonstrations and interventions. There are citizen journalists reporting news first hand -- from the scene of crimes, politicians off camera or grass roots meetings. These bloggers also function as watchdogs, whistleblowers and fact checkers. All this reporting is proto-democratic. It harbors the last vestiges of elitism and privileged access. It's the free press that enables democratic processes of decision-making and change. It does not function as every citizen's right to speak, vote and organize movements. It comes before that and makes democratic action possible.