The fact is, Posterous tried and lost. By all accounts, valiantly.
I find myself nodding when Maciej writes "Don't Be A Free User", because he is competing with free (and also because I want him to give me a tour of his vault of golden coins). Pointing out that your pricing scheme makes you a sustainable competitive alternative is fair.
But to the best of my knowledge, you aren't competing with Posterous. Why do you feel the need to rub this in?
I sincerely apologize if I'm just missing some parodic element of this post.