I think one of the reasons I stopped using Tumblr for general blogging was because it didn't autosave while I was writing my long posts. I think there are a lot of holes in the walls of houses around the world because of this.
That's actually one of the things Tumblr does right. If you close out of a post before you publish it, you'll get a notice on your dashboard to either continue editing it or discard it.
