The problem with blogs is that they don't know what they are yet. They're less a genre than a form, like books. You can't talk about how to write books without talking about what kind of book you're trying to write. Blogs can be about fashion, politics, science, academic subjects, fart jokes, getting in shape, or your grade eight camping vacation in Algonquin park. As with any other type of writing, the meaning and intention drive the choices. Or they should.
Let's pretend we're restricting ourselves to the 60-80% of blogs which are loosely called personal blogs--blogs about the writer's life. This immediately catapults into another problem: What is the meaning? That is, what is the writer trying to say? And why are they trying to say it--what is their intention?
Most blogs aren't really memoir.
I went into the bookstore last week (after Mad's question) and had a look over the memoirs on offer. There are memoirs about having a facial disfigurement, memoirs about travelling in France, memoirs about growing up in a cult, memoirs about being famous; they are told in first-person prose, as a graphic novel, as a series of short essays or stories. In fact the only thing that they have in common is that they are about something. The memoirist has a story they want to share. A story. One.
Some blogs fall into this category; but even most blogs that begin this way eventually become a place where the blogger can (and does) talk about whatever comes into their head.
Also, memoirs are events told from enough distance that an underlying story can be discerned and a shape brought to the material. In The Art of Time in Memoir: Then, Again, Sven Birkets argues that the distinguishing feature of the memoir is the layering of present and past, the past seen through the clarifying lens of the present. The past interpreted and shaped by the knowledge and wisdom gained since. This, obviously, is difficult when the past in question is this morning over breakfast. One could argue that blogs aspiring to be memoirs are in the process of becoming, distilling events into the meaningful experiences used to shape a memoir.
A number of years ago I came across a tantalizing reference to "The Pillow Book of Sei Shonagon" in a craft book on art journaling: "Sei Shonagon began writing her journal in an informal notebook style that is known as makura no soshi, or pillow book style. Yet even her informal writing was done in such a pure form of prose that it is considered a model of good style. Although she began her journal in private, it was soon ciruclated at court because of its elegant style and witty, beautifully written contents. Once her book became well known, Shonagon began writing in a more self-conscious manner, with an awareness that her pillow book would be read by the public. She was an excellent and detached observer of her own culture." (I've since managed to find the pillow book online.)
My perspective is that the personal blog is usually a modern-day pillow book, or a diary written for an extended audience. The structure of a pillow book allows for a series of short entries on disparate topics, the only common thread in which is the person who wrote them. Anyone therefore who believes that this idea of writing a diary for the public is some kind of twisted new-fangled narcisissistic practice that heralds the decline of western civilization or possibly the end of the world as we know it is, quite simply, wrong.
1. Meaning, intention and function still apply. What are you trying to say in a post, why are you trying to say it, and what is the best way to do so?
2. Structurally, stylistically and functionally, memoirs are indistinguishable from fiction.
Characters are engaged in a struggle to get something they want, which culminates in a climax, following which comes some sort of insight (not all fiction does this, but it does seem to be a requirement of memoir--if not for the protagonist, then at least for the reader). Memoir works the same way fiction works; by creating an empathetic bond between the main character and the reader so that the reader can understand the protagonist's experience and, through that, the underlying meaning.
Memoir introduces important ethical considerations not present in fiction (how close to stick to the truth? How much right do you have to share someone else's story? How reliable is memory?): but none of those change the underlying structure or function, or the means used to achieve them (dialogue, scene-setting, narrative arc, etc.).
3. Pillow books are a lost art-form in the west. We have public diaries--Anne Frank, Henry James's sister, etc.--but they weren't intended to be public. This gives bloggers very few models to build on.
All of this assumes that the meanings and intentions of personal blogs and blog posts are restricted essentially to pillow book vs. memoir; of course that's not true. Just off the top of my head I can think of some personal blogs that function more like email, even phonecalls. And as commenters have already pointed out, there are some blogs where the entire apparent function is to build a cult of personality around the blogger, to unite in a shared appreciation of something underground (eg. Will Wheaton), in which case literature doesn't come into it--what would the equivalent of that be? Reality TV? The Rocky Horror Picture Show?
But let's keep this simple. Simpler. Let's keep this to territory I know something about (though if someone else wants to tackle the other genres, either here or on their own blogs, that would be great) and look at the pillow book diarists and memoirists of personal blogging. Another day.