Why would you ever want to do this?

Migrate from Wordpress to Posterous?

I fancied a change..

Funny, I'd like to move more of my stuff to Wordpress. Though I've not used Posterous in quite some time.

I just fancied going down the hosted route for a change, less maintenance, no comment spam to worry about, besides I didn't need half the features Wordpress offers.

There are a couple of feature that Posterous could do with though, like custom slug, easier comment handing, javascript. I'll manage though, it's a nice change for now.

Purely out of curiosity, why Posterous over Wordpress.com?

I didn't like the idea of paying for certain features, mainly to use my own domain. I'm not sure if it'll be a permanent move yet so didn't want to pay only to decide to go back to self hosted somewhere down the line.

Does this really read in an entire xml file of all your posts for every request, just to redirect? Seems inefficient. I think redis might be a good fit for this.

It is pretty inefficient but I didn't have masses of posts to migrate so it made sense. If this were anything more than a quick and dirty script then a data store would be the best approach, maybe sqlite.