Working my way through this. I think I have the solution for us.
If you self-host WP on your domain, I think the robots.txt 'no index' is the best way to go.
If you're using a Wordpress.com blog (blog is hosted by WP), go to "Settings" on the bottom of the left sidebar.
Privacy > Hidden "Your site is visible to everyone, but we ask search engines to not index your site."
That's probably as good as it gets, folks. I'm confident trustworthy search engines will respect that setting and that should take care of any SEO/duplicate content issues.
I think that @yabdab's intention was for this to be another option for blogging in RW instead of the plugin or other 3P solutions. It's solid, and well implemented.