The guys at Posterous have been adding a lot more features since this post was made. One new and exciting one for many people here will be:
Posterous Now Supports Drupal Blogs
I've set up a few clients that way, and also some that blog by SMS from their mobile phone. Don't know about 'autopost to everywhere', as I don't do social networking for clients, but that sounds very useful for people interested in that sort of thing.
I mentioned my new blog in another post. It is hosted on a fairly new service, Posterous. The thing that attracted me to it was that it allowed me to blog easily from email. They are continually working on new features, and have a few that I thought you might like to know about.
The "Autopost to Everywhere" concept is very useful. When you post to Posterous, you have have your post title and a link to the post sent to your Twitter feed. If you added any photos, they can be added to your Flickr feed. You can have your blog post added to a Tumblr, Blogger, Wordpress.com, Typepad, Livejournal or Xanga blog, and any other blog that supports the MetaWebLog API and Really Simple Discovery.
So you could use Posterous to post to almost any pre-existing blog you might have, all from a simple email, which may be useful for you.