> 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.
You run into the same problem you had with Posterous. Having your own domain does nothing to prevent Tumblr from running out of cash and shutting down your blog. Luckily Twitter/Posterous are doing the right thing by providing a way to retain control of your data. Imagine if they didn't provide those tools, you're at the mercy of the platform.
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.
I use both tumblr and Jekyll, but I think it's pretty low risk that tumblr will vanish without any warning. We've known posterous would disappear for a while now. And if you point an rss reader at any blog you get a pretty decent backup trivially, so it's a hassle if tumblr disappears but not catastrophic.
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.