> Money isn’t that pressing an issue–yet. Karp says Tumblr has banked “most of” the $125 million it has raised. But Tumblr spent an estimated $25 million on its operation last year and will likely have to shell out up to $40 million this year. In 2013 David Karp has a race on his hands: Can he break into the black before needing to hold his hand out again for investors?
The mobile tools for Tumblr are definitely a plus. But if you aren't blogging at a rate that requires you to have scheduling tools, then I wonder if it'd just be easier to set up a Jekyll powered blog. You lose the social-network effect of Tumblr (the reblogs and like), but from what I've seen, it's visual blogs that get reblogged/liked the most, because of how users interact (and see things) in their dashboard.
I'm not on Posterous, but I am on Tumblr and I do worry the company won't always be around once the cash runs dry or they get acquihired.
I like the WordPress strategy of strong data portability features within a hosted environment and an open source, self-hosted option. This way even if WordPress.com (Automattic) gets acquired, WordPress.org will always be an option without having to get comfortable with an entirely new platform. Of coarse, if you're a developer you could always just use an open source static site generator like Jekyll or Middleman.
But I am reluctant to use tumblr for semi-permanent content; I mostly use it for posts with a short shelf life. So maybe I agree with you subconsciously.