One advantage of posterous is you can post from email. Email is always easy to get to, so you can quickly share a link or comment that way. In fact, I'm currently writing this on my phone in the subway. It does raise security issues though. Do they make sure the email really originated from you? That's what I'll check next.
Update: When I sent an email from PHP, they saved it as a draft so I could confirm it was really me. So they don't have any gaping security hole.