Hi, I'm one of the cofounders of Posterous. I'm sorry we weren't able to save the site after the company was acquired. I left the company in 2011 over disagreements with my cofounder about strategy. It's a shame we couldn't do more.
I'm happy to say though that there's a new site I've created, called Posthaven. It's just like Posterous, and we're writing it from scratch, just me and another one of our Posterous cofounders Brett Gibson. It's $5/mo per user, and we pledge to keep the site online forever. This time, it's not about growth -- it's about sustaining the site and keeping it running, while making the best dang software we can.
I tried the Wordpress, SquareSpace and Tumblr options, and none of them did what I wanted. Here's my migration guide for Posterous alternatives, including Posthaven. There's detailed instructions on how to switch to another site, and what you do get and what you don't.
Switch to Posthaven -- you only have a few days left.
I personally guarantee we will bring back everything you liked about Posterous. Because we wrote much of it the first time, and we'll make it even better this time.
-Garry Tan
Former cofounder, Posterous
Cofounder, Posthaven
Partner, Y Combinator