Posterous is shutting down in a week and the Archive Team needs more time else 1.3 million blogs will essentially disappear.
I've been following an exchange between Jason Scott (Archive Team / Internet Archive) and Sachin Agarwal (Posterous) .
It appears that Posterous gave the Archive Team some dedicated servers to hit but it wasn't sufficient to download the amount that's going to be deleted.
I don't know all of the details but saving content to a historical archive is invaluable. Offering the ability for users to download their content is great but it serves a very different purpose than what the Archive Team and Internet Archive does.
Additionally, it's certain that much of the content will disappear because users didn't receive the shutdown email, 30 days wasn't long enough or simply didn't bother to do anything. The public content there is still valuable.