This would be a great plugin, I’ll pay if someone can develop it so that its simple for the end user (multiblog owner) to implement and add authors without having to do complex RSS stuff.
The best way I can see to do it is the create an RSS feed for each author (if they each have a category on one blog) and then use FeedWordPress or other RSS plugin and essentially syndicate it to the other blogs. You’d have to make sure that the author was only posting the article to one of the blogs in your “network” or you’d end up with a bunch of duplicate cross-postings. That’s the long way around I suppose.
Let me know if you figure anything out.
Chris