Wow,
I finally got all of my blogs from different sites imported into Posterous. I was having the worst trouble trying to get Posterous to import my Tumblr blog. I instead had to have it exported to a Wordpress xml file and then upload that xml file for the import. Everything seems to have worked though with only minor editing needed.
I do have to say though that Posterous' help was pretty poor throughout this whole process. Let's hope that is not a hint of things to come for the future use of Posterous. I migrated away from Tumblr because of its downtime and issues I had with the site loading.