Wordpress and Posterous are designed by geeks. Tumblr is designed by a nongeek.

First off, Tumblr is not primarily a blog. It's what we call a "tumblelog", which is a stupid word; I like to call it "vomit" or "spew". The fact that it's the sleekest blog platform out there is secondary to its larger function as a spewing platform.

Blogs are for creating. Spew is for recycling, for breaking things down into small teeny pieces, for streams and streams of things which are essentially meaningless but contribute to a larger whole. Now, not all blogs are strictly bloglike either; the Linked List format is somewhat in between the two, though Linked Lists are usually more disciplined in nature. Another way to draw the distinction is to say that blogs are for building things, while tumblelogs are for shaping them. Or you could call blogs classical music and tumblelogs jazz. One is looser, more freeform, more about the movement than about the individual notes. The other is about the finished product, or about realizing a vision.

A defining characteristic of a true geek is that he builds. Doesn't matter what he builds; what matters is that he appreciates structures. So when we look at a blogging platform, our needs traditionally tend to be focused on constructing more elaborate things. They also tend to be relatively solitary in nature. (Wordpress is; I never had a friend that used Posterous and so I don't know how they handle following things.)

I like slagging on Posterous because I'm still bothered that they get compared to Tumblr when they're really entirely different. Tumblr's breakthrough was its deconstruction of the blog format. You could post an image without a title. You could post a quote without something to frame it. You could post ANYTHING without a datestamp, or a "posted by" attribute, because nobody cares about them, they just care about the flow of content. Posterous has lines of datestamping, and they don't handle title-less posts. They're all about traditional title-body posting. They're all about "blogs", about these elaborate constructions. They aren't broken down like Tumblr.

Tumblr's a fucking awesome engine because it removes everything bloggy about blogs. It's designed for a steady vomitstream of thoughts and ideas. Not your thoughts or ideas. Anybody's. And it strips away everything we associate with blogs, and with everything it strips away it becomes sleeker, lither, more powerful. No comments means no conversations other than reblogs — and reblogs are great because first off, they let you improvise off anybody else's stream, and second off, they make it IMPOSSIBLE to participate without being a "primary creater" with a flow that other people are following, versus blog comments where every commenter is attached to one site at a time.

That means it attracts people who don't build things. People who just want to push out content without worrying about being judged for value. But they want to push it out, because it is a creative and cathartic act just to release these ideas out into the world, or to change their flow. Lower barrier to entry, more ability to interact meaningfully. You can participate without any skill but still find that people are interested in you.

Now, I use Tumblr primarily as a building tool. I find that its theming system makes it very easy for me to design custom interfaces for complex publishing sites, and yet still push through the entire site as a streaming feed to any Tumblr user who wants it. And it's used by lots of serious designers who appreciate its versatility. But I'm an edge user. Every HN user here who uses Tumblr is an edge users. The real users don't post here, because they're not out to build things, they're out to just express themselves loudly and with fury.