But Posterous isn't a serious blog engine. It is by very loose definitions of "blog engine" but it's a service trying to do stuff that Wordpress and Typepad don't do. I don't like comparing it dead-on to Wordpress. If you did, Wordpress would come plenty short in a lot of ways.

This is a great feature to have, particularly the Tumblr importing option. There're plenty of disgruntled Tumblr users right now looking for a way out.