I viewed Matt's 2012 and 2013 State of the Word addresses and both years he mentioned the attrition rate of WP.
I think a quick start guide would be a good idea for new users.
It could be something like,
Your First Rodeo with WordPress or
Your Quick and Dirty guide to WordPress
or Down on the Farm with WordPress.
It could be info available after the installation process and it would only be 5-8 pages long. Make it downloadable incase new user wants to save/print it to follow along.
It could highlite all the most basic settings to get your blog/site up and running.
Then as they were using it, if they wanted to get more indepth, there could be links to the setting to learn more.
Each setting could have an associated item: For example if a rodeo theme was chosen, the site would be the arena. A cowboy could represent the user, the bull would be the appearance setting, the rodeo clown could represent the pages etc....
The documentation is stellar now but there is so much there it is hard to know where to start. Even the topics Getting Started and New to WP contain so much for a new user.
This user guide would be designed to get the new user up and running and not get discouraged and walk away.