I was able to download my Posterous archive.
http://static.scripting.com/dave/daveWinerPosterousArchive.zip
I'm busy with other projects, but wanted to be sure I could find this if I find time to move it to another location.
I took a brief look inside, and it looks fine. The posts are stored as RSS 2.0 items. Shouldn't be hard for any experienced blogging software developer to work with this.
