Maybe my use case is weird, but I found Posterous annoying. I tried to use it over and over and every time I hit some weird limitation that kept me from doing what I wanted.

The final straw was posting code. Tumblr makes that stupid easy (since they accept Markdown), so I can just do that instead of trying to figure out the magic incantation to make it work on Posterous (gists or something? I don't know. It wasn't documented when I last tried).