A lot of us, not all of us, but a lot, have multiple blogs.
WordPress MU is a solution, but not entirely as simple as what I'm thinking, because would if these multiple blogs exist across multiple servers, and it is impossible to combine them, or just way too much of a hassle.
We may not want an interface to control everything about our blogs in multiple places, would if we only want to be able to post to multiple blogs simultaneously?
Instead of constantly logging in, copy/paste, etc...
This could all be taken care of with a simple blog associations table.
Essentially the way all the other API's out there interface with WordPress blogs, or really any blog interface.
You should be able to register your blogs within your blogs.
It just makes sense.
All it needs is a URI, a username, and a password (The URI and the username combined would be the index).
Maybe some extra meta if you want for title, description, etc..
Then when in your edit post page, there just needs to be another content block for "Post to another Blog", there is all your registered blog associations in a table, and you just have to check which ones you will post to when saving the current post.
Everything seems to be ready for this to happen pretty easily.
I might even do it with a plugin if I have the time.